ALBERT

Description: New sedimentological data of facies and diagenesis as well as chronological data including strontium (87Sr/86Sr)-isotope ratios and uranium (U)-series dating, radiocarbon (14C) accelerator mass spectrometry (AMS) dating and biostratigraphy from elevated reef terraces (makatea) in the southern Cook Islands of Mangaia, Rarotonga and Aitutaki contribute to controversial discussions regarding age and sea-level relationships of these occurrences during the Neogene and Quaternary. The oldest limestones of the uplifted makatea island of Mangaia include reef-related facies which are mid-Miocene in age, based on new Sr-isotope and biostratigraphical data. In between these older deposits and the lowest coastal reef terrace of marine isotope stage (MIS) 5e, various older Pleistocene reef-related facies were identified. Based on Sr-isotope ratios, these were deposited during earlier Pleistocene highstands (as old as 2.28 Ma). Rare reef terraces on Rarotonga belong to the Plio-Pleistocene and the late Miocene, according to 87Sr/86Sr ratios. The late Miocene age is enigmatic as it exceeds the age of subaerially exposed volcanic rocks of Rarotonga island. The fossil reef could have formed on an older submarine volcanic high that was later displaced by younger volcanism to its present position, or the Sr-age could be too old due to diagenetic resetting. The Plio-Pleistocene Rarotonga reef terraces are overlain irregularly by Holocene reef deposits that are interpreted as storm rubble. Reef terraces on Aitutaki represent evidence of a higher-than-present (up to 1 m) sea-level during the late Holocene, based on 14C AMS age data. They are very similar to elevated late Holocene reefs of adjacent French Polynesia with regard to composition, elevation and age.

Description: The present study aims to valorize the apple peels (AP) and grape seeds (GS) by the fortification of the yogurts using their powder. Firstly, the optimization of the extraction parameters for assessing maximum of total phenolic content (TPC) was achieved. Under the optimized conditions, the experimental maximum yields of TPC were 19.33 ± 2.33 and 240.59 ± 4.77 mg Gallic Acid Equivalents (GAE)/100 g Dry Weight (DW) for AP and GS, respectively, which was in close agreement with predicted values (19.32 ± 0.91 and 242.26 ± 11.08 mg GAE/100 g DW for AP and GS, respectively). The antioxidant capacity of GS extract was better with IC50 of 12.22 ± 0.89 and 225.47 ± 7.10 µg/ml in DPPH and phosphomolybdenum assays, respectively. Besides, powder from these by-products was incorporated into yogurt samples. The classification test revealed that the yogurt prepared with GS powder was the preferred one.

Description: The present study investigates the response of the high-latitude carbon cycle to changes in atmospheric greenhouse gas (GHG) concentrations in idealized climate change scenarios. To this end we use an adapted version of JSBACH – the land surface component of the Max Planck Institute for Meteorology Earth System Model (MPI-ESM) – that accounts for the organic matter stored in the permafrost-affected soils of the high northern latitudes. The model is run under different climate scenarios that assume an increase in GHG concentrations, based on the Shared Socioeconomic Pathway 5 and the Representative Concentration Pathway 8.5, which peaks in the years 2025, 2050, 2075 or 2100, respectively. The peaks are followed by a decrease in atmospheric GHGs that returns the concentrations to the levels at the beginning of the 21st century, reversing the imposed climate change. We show that the soil CO2 emissions exhibit an almost linear dependence on the global mean surface temperatures that are simulated for the different climate scenarios. Here, each degree of warming increases the fluxes by, very roughly, 50 % of their initial value, while each degree of cooling decreases them correspondingly. However, the linear dependence does not mean that the processes governing the soil CO2 emissions are fully reversible on short timescales but rather that two strongly hysteretic factors offset each other – namely the net primary productivity and the availability of formerly frozen soil organic matter. In contrast, the soil methane emissions show a less pronounced increase with rising temperatures, and they are consistently lower after the peak in the GHG concentrations than prior to it. Here, the net fluxes could even become negative, and we find that methane emissions will play only a minor role in the northern high-latitude contribution to global warming, even when considering the high global warming potential of the gas. Finally, we find that at a global mean temperature of roughly 1.75 K (±0.5 K) above pre-industrial levels the high-latitude ecosystem turns from a CO2 sink into a source of atmospheric carbon, with the net fluxes into the atmosphere increasing substantially with rising atmospheric GHG concentrations. This is very different from scenario simulations with the standard version of the MPI-ESM, in which the region continues to take up atmospheric CO2 throughout the entire 21st century, confirming that the omission of permafrost-related processes and the organic matter stored in the frozen soils leads to a fundamental misrepresentation of the carbon dynamics in the Arctic.

Description: A realistic simulation of the surface mass balance (SMB) is essential for simulating past and future ice-sheet changes. As most state-of-the-art Earth system models (ESMs) are not capable of realistically representing processes determining the SMB, most studies of the SMB are limited to observations and regional climate models and cover the last century and near future only. Using transient simulations with the Max Planck Institute ESM in combination with an energy balance model (EBM), we extend previous research and study changes in the SMB and equilibrium line altitude (ELA) for the Northern Hemisphere ice sheets throughout the last deglaciation. The EBM is used to calculate and downscale the SMB onto a higher spatial resolution than the native ESM grid and allows for the resolution of SMB variations due to topographic gradients not resolved by the ESM. An evaluation for historical climate conditions (1980–2010) shows that derived SMBs compare well with SMBs from regional modeling. Throughout the deglaciation, changes in insolation dominate the Greenland SMB. The increase in insolation and associated warming early in the deglaciation result in an ELA and SMB increase. The SMB increase is caused by compensating effects of melt and accumulation: the warming of the atmosphere leads to an increase in melt at low elevations along the ice-sheet margins, while it results in an increase in accumulation at higher levels as a warmer atmosphere precipitates more. After 13 ka, the increase in melt begins to dominate, and the SMB decreases. The decline in Northern Hemisphere summer insolation after 9 ka leads to an increasing SMB and decreasing ELA. Superimposed on these long-term changes are centennial-scale episodes of abrupt SMB and ELA decreases related to slowdowns of the Atlantic meridional overturning circulation (AMOC) that lead to a cooling over most of the Northern Hemisphere.

Description: Variability of surface water masses of the Laptev and the East Siberian seas in August–September 2018 is studied using in situ and satellite data. In situ data were collected during the ARKTIKA-2018 expedition and then complemented with satellite-derived sea surface temperature (SST), salinity (SSS), sea surface height, wind speed, and sea ice concentration. The estimation of SSS fields is challenging in high-latitude regions, and the precision of soil moisture and ocean salinity (SMOS) SSS retrieval is improved by applying a threshold on SSS weekly error. For the first time in this region, the validity of DMI (Danish Meteorological Institute) SST and SMOS SSS products is thoroughly studied using ARKTIKA-2018 expedition continuous thermosalinograph measurements and conductivity–temperature–depth (CTD) casts. They are found to be adequate to describe large surface gradients in this region. Surface gradients and mixing of the river and the sea water in the ice-free and ice-covered areas are described with a special attention to the marginal ice zone at a synoptic scale. We suggest that the freshwater is pushed northward, close to the marginal ice zone (MIZ) and under the sea ice, which is confirmed by the oxygen isotope analysis. The SST-SSS diagram based on satellite estimates shows the possibility of investigating the surface water mass transformation at a synoptic scale and reveals the presence of river water on the shelf of the East Siberian Sea. The Ekman transport is calculated to better understand the pathway of surface water displacement on the shelf and beyond.

Description: Pa.ra.rho.do.spi.ril'lum. Gr. pref. para-, beside, alongside of, near, like; N.L. neut. n. Rhodospirillum, a bacterial generic name; N.L. neut. n. Pararhodospirillum, resembling Rhodospirillum. Proteobacteria / Alphaproteobacteria / Rhodospirillales / Rhodospirillaceae / Pararhodospirillum Pararhodospirillum species are spiral-shaped, mesophilic, and phototrophic freshwater bacteria of the Rhodospirillaceae family. Cells are motile by polar flagella, and photosynthetic pigments are located in internal photosynthetic membranes present as lamellar stacks. Photosynthetic pigments are bacteriochlorophyll a and carotenoids of the spirilloxanthin series with spirilloxanthin itself lacking. Ubiquinone-9 and rhodoquinone-9 are the major quinones. All species are sensitive to oxygen and require anoxic or microoxic conditions for growth. They grow photoheterotrophically under anoxic conditions in the light. Photoautotrophic growth, aerobic chemotrophic growth, and fermentative growth have not been demonstrated. Growth factors are required. DNA G + C content (mol%): 60.2–65.8 (Bd and HPLC) and 64.7–67 (GA). Type species: Pararhodospirillum photometricum Lakshmi et al. 2014VP (basonym: Rhodospirillum photometricum Molisch 1907AL).

Description: Rho.do.ci'sta Gr. neut. n. rhodon, rose; L. fem. n. cista a basket; N.L. fem. n. Rhodocista, red basket. Proteobacteria / Alphaproteobacteria / Rhodospirillales / Azospirillaceae / Rhodocista Rhodocista centenaria is a well-characterized thermotolerant, phototrophic purple bacterium growing optimally at a temperature of 40–45°C and a maximal growth temperature of 48°C. Under low nutrient conditions, Rhodocista forms desiccation-, heat-, and UV-resistant cysts, which enable survival under severe drought and salt stress. Cells are motile by a single polar flagellum in liquid culture but in addition form lateral flagella on agar surfaces and under these conditions may show a characteristic phototactic movement. Rhodocista species grow under photoheterotrophic conditions and also are able to perform a chemotrophic aerobic metabolism. They encode enzymes for autotrophic carbon dioxide fixation and fixation of dinitrogen, although autotrophic growth has so far not been demonstrated. In the type species, bacteriochlorophyll biosynthesis occurs under both aerobic and anaerobic growth conditions. Aerobically grown cells are fully pigmented. In other species, oxygen may inhibit photosynthetic pigment biosynthesis, and aerobically grown cells are colorless. DNA G + C content (mol%): 68.8–69.9 (Tm), 70.5 (WGS). Type species: Rhodocista (Rcs.) centenaria Kawasaki et al. 1992, VL48 (basonym: Rhodospirillum centenum Favinger et al. 1989, VL48).

Description: Rho.do.pi'la. Gr. neut. n. rhodon the rose; N.L. fem. n. pila a ball or sphere; N.L. fem. n. Rhodopila red sphere. Proteobacteria / Alphaproteobacteria / Rhodospirillales / Acetobacteraceae / Rhodopila Rhodopila globiformis is one of the very few anaerobic phototrophic purple bacteria that can grow below pH 6 with an optimum depending on the organic carbon substrate from 4.8 to 5.6. Growth occurs preferably photoheterotrophically under anoxic conditions in the light. Cells are sensitive to oxygen but grow by respiration under microoxic conditions in the dark. Growth factors are required. They are acidophilic freshwater bacteria that inhabit acidic warm sulfur springs. Cells are spherical to ovoid, motile by means of polar flagella, and divide by binary fission. They stain Gram-negative and have internal photosynthetic membranes of the vesicular type. Rhodopila is classified within the Acetobacteraceae family and Rhodospirillales order of the Alphaproteobacteria. The photosynthetic pigments are bacteriochlorophyll a and carotenoids. The major fatty acids are C18:1 (∼75%) and C16:0. Ubiquinones, menaquinones, and rhodoquinones with 9 and 10 isoprene units are produced. DNA G + C content (mol%): 67.1 (genome analysis). Type species: Rhodopila globiformis Imhoff et al. 1984VP (basonym: Rhodopseudomonas globiformis Pfennig 1974AL).

Description: Rho.do.pla'nes. Gr. neut. n. rhodon rose; Gr. masc. n. planos a wanderer; N.L. masc. n. Rhodoplanes a red wanderer. Proteobacteria / Alphaproteobacteria / Rhizobiales / Hyphomicrobiaceae / Rhodoplanes The genus Rhodoplanes accommodates species of anoxygenic facultative phototrophic bacteria that grow optimally under anaerobic conditions in the light. They belong to the family Hyphomicrobiaceae of the order Rhizobiales within the class Alphaproteobacteria. Cells are Gram-stain-negative rods and multiply by budding and asymmetric cell division. Motile by means of polar, subpolar, or lateral flagella. Internal photosynthetic membranes are present as lamellar stacks parallel to the cytoplasmic membrane. Photosynthetic pigments are bacteriochlorophyll a and carotenoids of the spirilloxanthin series. Photoorganotrophy with pyruvate and some other organic acids is the best mode of growth. Straight-chain, monounsaturated C18:1 ω7c is the main component of the cellular fatty acids and C16:0 is a second major component. Ubiquinones and rhodoquinones with 10 isoprene units (Q-10 and RQ-10) are present. The main components of polar lipids are phosphatidylethanolamine, phosphatidylcholine, phosphatidylglycerol, and diphosphatidylglycerol. Terrestrial and freshwater bacteria having a preference for mesophilic to moderately thermophilic habitats and neutral pH. DNA G + C content (mol%): 67.2–70.4. Type species: Rhodoplanes roseus Hiraishi and Ueda 1994 (Rhodopseudomonas rosea Janssen and Harfoot 1991).

Description: Rho.do.pi'la. Gr. neut. n. rhodon the rose; N.L. fem. n. pila a ball or sphere; N.L. fem. n. Rhodopila red sphere. Proteobacteria / Alphaproteobacteria / Rhodospirillales / Acetobacteraceae / Rhodopila Rhodopila globiformis is one of the very few anaerobic phototrophic purple bacteria that can grow below pH 6 with an optimum depending on the organic carbon substrate from 4.8 to 5.6. Growth occurs preferably photoheterotrophically under anoxic conditions in the light. Cells are sensitive to oxygen but grow by respiration under microoxic conditions in the dark. Growth factors are required. They are acidophilic freshwater bacteria that inhabit acidic warm sulfur springs. Cells are spherical to ovoid, motile by means of polar flagella, and divide by binary fission. They stain Gram-negative and have internal photosynthetic membranes of the vesicular type. Rhodopila is classified within the Acetobacteraceae family and Rhodospirillales order of the Alphaproteobacteria. The photosynthetic pigments are bacteriochlorophyll a and carotenoids. The major fatty acids are C18:1 (∼75%) and C16:0. Ubiquinones, menaquinones, and rhodoquinones with 9 and 10 isoprene units are produced. DNA G + C content (mol%): 67.1 (genome analysis). Type species: Rhodopila globiformis Imhoff et al. 1984VP (basonym: Rhodopseudomonas globiformis Pfennig 1974AL).

Description: Rho.do.spi.ril'lum. Gr. neut. n. rhodon, the rose; N.L. neut. n. Spirillum, a bacterial genus; N.L. neut. n. Rhodospirillum, the rose Spirillum. Proteobacteria / Alphaproteobacteria / Rhodospirillales / Rhodospirillaceae / Rhodospirillum The genus Rhodospirillum has harbored a diverse set of spiral-shaped phototrophic bacteria, most of which have been reclassified as species of other genera, families, and even orders and phyla since the 1980s. The heterogeneity has been long known, but only the faith into sequence-based information gave strong support for taxonomic rearrangements. Currently, the genus Rhodospirillum contains a single species, which is characterized by spiral-shaped cells, motility by bipolar flagella, and internal membranes as vesicles. It performs anaerobic photosynthesis, which is restricted to anoxic light conditions due to the oxygen-sensitive biosynthesis of bacteriochlorophyll and thus the phototrophic apparatus. It can grow photoheterotrophically as well as photoautotrophically. The key enzyme of autotrophic carbon dioxide fixation in Rhodospirillum rubrum, ribulose bisphosphate carboxylase (RubisCO) type-II, is well characterized and forms a homodimer that is also encoded in some related genera of Rhodospirillaceae. Chemotrophic growth may also occur under microoxic to oxic conditions in the dark and anaerobically by fermentation. The genus comprises mesophilic freshwater bacteria. Ubiquinones and rhodoquinones with 10 isoprene units and fatty acids typical of other Alphaproteobacteria with C18:1, C16:0, and C16:1 as major components are present. DNA G + C content (mol%): 64.6–65.7, type 65.4 (genome analysis), 63.8–65.8 (Bd). Type species: Rhodospirillum (Rsp.) rubrum Molisch 1907AL (basonym: Spirillum rubrum Esmarch 1887).

Description: Rho.do.ci'sta Gr. neut. n. rhodon, rose; L. fem. n. cista a basket; N.L. fem. n. Rhodocista, red basket. Proteobacteria / Alphaproteobacteria / Rhodospirillales / Azospirillaceae / Rhodocista Rhodocista centenaria is a well-characterized thermotolerant, phototrophic purple bacterium growing optimally at a temperature of 40–45°C and a maximal growth temperature of 48°C. Under low nutrient conditions, Rhodocista forms desiccation-, heat-, and UV-resistant cysts, which enable survival under severe drought and salt stress. Cells are motile by a single polar flagellum in liquid culture but in addition form lateral flagella on agar surfaces and under these conditions may show a characteristic phototactic movement. Rhodocista species grow under photoheterotrophic conditions and also are able to perform a chemotrophic aerobic metabolism. They encode enzymes for autotrophic carbon dioxide fixation and fixation of dinitrogen, although autotrophic growth has so far not been demonstrated. In the type species, bacteriochlorophyll biosynthesis occurs under both aerobic and anaerobic growth conditions. Aerobically grown cells are fully pigmented. In other species, oxygen may inhibit photosynthetic pigment biosynthesis, and aerobically grown cells are colorless. DNA G + C content (mol%): 68.8–69.9 (Tm), 70.5 (WGS). Type species: Rhodocista (Rcs.) centenaria Kawasaki et al. 1992, VL48 (basonym: Rhodospirillum centenum Favinger et al. 1989, VL48).

Description: Rho.do.tha.las.si.a.ce'ae. N.L. neut. n. Rhodothalassium, type genus of the family; suff. -aceae, ending to denote a family; N.L. fem. pl. n. Rhodothalassiaceae, the family of Rhodothalassium. Proteobacteria / Alphaproteobacteria / Rhodothalassiales / Rhodothalassiaceae Cells are vibrioid to spiral shaped, are motile by means of polar flagella, and multiply by binary fission. They belong to the class Alphaproteobacteria and stain Gram-negative. An unusual protein-rich cell wall with only low amounts of peptidoglycan may be present. Internal photosynthetic membranes are present as lamellar stacks lying parallel to the cytoplasmic membrane. The photosynthetic pigments are bacteriochlorophyll a and carotenoids. The major ubiquinone and menaquinone components are Q-10 and MK-10. Growth occurs preferably photoheterotrophically under anoxic conditions in the light but also may be possible under microoxic to oxic conditions in the dark. Obligately halophilic bacteria that require NaCl or sea salt for growth. Habitats are anoxic zones of hypersaline environments such as salterns, salt lakes, and evaporated coastal lagoons that are exposed to light. At present, the family includes a single genus. DNA G + C content of the type species and genus (mol%): 68.5–69.0 (genome analysis), 60.0–62.8 (HPLC analysis). Type genus: Rhodothalassium Imhoff et al. 1998VP.

Description: Phae.o.spi.ril'lum. Gr. masc. adj. phaeos, brown; N.L. neut. n. Spirillum, a bacterial genus; N.L. neut. n. Phaeospirillum, brown Spirillum. Proteobacteria / Alphaproteobacteria / Rhodospirillales / Rhodospirillaceae / Phaeospirillum Phaeospirillum species are vibrioid to spiral shaped and motile Alphaproteobacteria. They are strictly anaerobic and anoxygenic phototrophic bacteria with a reaction center and light-harvesting complexes located in the internal membrane stacks formed at a sharp angle with the cytoplasmic membrane. The photosynthetic pigments are bacteriochlorophyll a esterified with phytol and carotenoids of the spirilloxanthin series, with spirilloxanthin itself lacking. They have a photoheterotrophic metabolism and depend on anoxic conditions for biosynthesis of bacteriochlorophyll and photosynthesis. The preferred carbon substrates are fatty acids including longer chains up to pelargonate. The longer chain fatty acids provide a selective advantage for several of the species. Chemotrophic growth may be possible at controlled and very low oxygen tensions (〈1.5 kPa) in the dark. Ammonia and dinitrogen serve as nitrogen sources. Assimilatory sulfate reduction is present. Growth factors may be required. Phaeospirillum species are mesophilic freshwater bacteria with a preference for neutral pH that live in stagnant and anoxic freshwater habitats. DNA G + C content (mol%): 60.5–65.3 (Bd), 62.1–62.8 (Tm), 61.5–64.7 (WGS). Type species: Phaeospirillum (Phs.) fulvum Imhoff et al. 1998VP (basonym: Rhodospirillum fulvum van Niel 1944AL).

Description: Rho.do.tha.las.si.a'les. N.L. neut. n. Rhodothalassium, type genus of the order; suff. -ales, ending denoting an order; N.L. fem. pl. n. Rhodothalassiales, the Rhodothalassium order. Proteobacteria / Alphaproteobacteria / Rhodothalassiales The order currently comprises a single family and genus, which is characterized by halophilic anoxygenic phototrophic bacteria having spiral-shaped cells and containing lamellar photosynthetic membranes. The properties of the order are determined by the characteristics of the Rhodothalassiaceae family.

Description: Rho.do.tha.las'si.um. Gr. neut. n. rhodon, the rose; Gr. masc. adj. thalassios, belonging to the sea; N.L. neut. n. Rhodothalassium, the rose belonging to the sea. Proteobacteria / Alphaproteobacteria / Rhodothalassiales / Rhodothalassiaceae / Rhodothalassium The genus Rhodothalassium is represented by a single species and is the only genus of the Rhodothalassiaceae family and Rhodothalassiales order. It is characterized by vibrioid- to spiral-shaped cells which multiply by binary fission and are motile by means of flagella. Internal photosynthetic membranes are present as lamellar stacks lying parallel to the cytoplasmic membrane. Photosynthetic pigments are bacteriochlorophyll a and carotenoids of the spirilloxanthin series. Ubiquinones and menaquinones with 10 isoprene units (Q-10 and MK-10) are present. Growth occurs preferably photoheterotrophically under anoxic conditions in the light. Most strains also grow chemoorganotrophically under oxic conditions in the dark. Rhodothalassium species are obligately halophilic, require NaCl or sea salt for growth, and live in anoxic zones of hypersaline environments such as salterns, salt lakes, and evaporated coastal lagoons that are exposed to the light. DNA G + C content (mol%): 68.5–69.0 (WGS), 60.0–62.8 (HPLC). Type species: Rhodothalassium salexigens Imhoff et al. 1998VP (basonym: Rhodospirillum salexigens Drews 1981, VL9).

Description: Rho.do.pla'nes. Gr. neut. n. rhodon rose; Gr. masc. n. planos a wanderer; N.L. masc. n. Rhodoplanes a red wanderer. Proteobacteria / Alphaproteobacteria / Rhizobiales / Hyphomicrobiaceae / Rhodoplanes The genus Rhodoplanes accommodates species of anoxygenic facultative phototrophic bacteria that grow optimally under anaerobic conditions in the light. They belong to the family Hyphomicrobiaceae of the order Rhizobiales within the class Alphaproteobacteria. Cells are Gram-stain-negative rods and multiply by budding and asymmetric cell division. Motile by means of polar, subpolar, or lateral flagella. Internal photosynthetic membranes are present as lamellar stacks parallel to the cytoplasmic membrane. Photosynthetic pigments are bacteriochlorophyll a and carotenoids of the spirilloxanthin series. Photoorganotrophy with pyruvate and some other organic acids is the best mode of growth. Straight-chain, monounsaturated C18:1 ω7c is the main component of the cellular fatty acids and C16:0 is a second major component. Ubiquinones and rhodoquinones with 10 isoprene units (Q-10 and RQ-10) are present. The main components of polar lipids are phosphatidylethanolamine, phosphatidylcholine, phosphatidylglycerol, and diphosphatidylglycerol. Terrestrial and freshwater bacteria having a preference for mesophilic to moderately thermophilic habitats and neutral pH. DNA G + C content (mol%): 67.2–70.4. Type species: Rhodoplanes roseus Hiraishi and Ueda 1994 (Rhodopseudomonas rosea Janssen and Harfoot 1991).

Description: Pa.ra.rho.do.spi.ril'lum. Gr. pref. para-, beside, alongside of, near, like; N.L. neut. n. Rhodospirillum, a bacterial generic name; N.L. neut. n. Pararhodospirillum, resembling Rhodospirillum. Proteobacteria / Alphaproteobacteria / Rhodospirillales / Rhodospirillaceae / Pararhodospirillum Pararhodospirillum species are spiral-shaped, mesophilic, and phototrophic freshwater bacteria of the Rhodospirillaceae family. Cells are motile by polar flagella, and photosynthetic pigments are located in internal photosynthetic membranes present as lamellar stacks. Photosynthetic pigments are bacteriochlorophyll a and carotenoids of the spirilloxanthin series with spirilloxanthin itself lacking. Ubiquinone-9 and rhodoquinone-9 are the major quinones. All species are sensitive to oxygen and require anoxic or microoxic conditions for growth. They grow photoheterotrophically under anoxic conditions in the light. Photoautotrophic growth, aerobic chemotrophic growth, and fermentative growth have not been demonstrated. Growth factors are required. DNA G + C content (mol%): 60.2–65.8 (Bd and HPLC) and 64.7–67 (GA). Type species: Pararhodospirillum photometricum Lakshmi et al. 2014VP (basonym: Rhodospirillum photometricum Molisch 1907AL).

Description: Ro.se.o.spi'ra. L. masc. adj. roseus, rosy; Gr. fem. n. spira, the spiral; N.L. fem. n. Roseospira the rosy spiral. Proteobacteria / Alphaproteobacteria / Rhodospirillales / Rhodospirillaceae / Roseospira Roseospira species are vibrioid to spiral shaped, anoxygenic, and phototrophic bacteria of the Rhodospirillaceae family that live in various types of marine and slightly saline habitats all over the world. The photosynthetic pigments are bacteriochlorophyll a and carotenoids of the spirilloxanthin series, and internal photosynthetic membranes are present as vesicles. They perform a phototrophic way of life using organic substrates (photoheterotrophic growth) or inorganic reduced sulfur compounds (photoautotrophic growth) as electron donors for photosynthesis. Bacteriochlorophyll biosynthesis depends on anoxic to microoxic conditions, and chemotrophic growth is possible under microoxic to oxic conditions in the light. Nitrogenase and ribulose bisphosphate carboxylase may be present. Vitamins or yeast extracts are required as growth factors. The G + C content of the DNA is 67.8–71.2 (GA), and the genome size ranges from 4.19 to 4.61 Mb. DNA G + C content (mol%): 67.8–71.2 (GA) (type species 66.6 Tm). Type species: Roseospira mediosalina Imhoff et al. 1998VP (synonym: “Rhodospirillum mediosalinum” Kompantseva and Gorlenko 1984).

Description: Although numerous pollen records are available worldwide in various databases, their use for synthesis works is limited as the chronologies are, as yet, not harmonized globally, and temporal uncertainties are unknown. We present a chronology framework named LegacyAge 1.0 that includes harmonized chronologies of 2831 palynological records (out of 3471 available records), downloaded from the Neotoma Paleoecology Database (last access: April 2021) and 324 additional Asian records. All chronologies use the Bayesian framework implemented in Bacon version 2.5.3. Optimal parameter settings of priors (accumulation.shape, memory.strength, memory.mean, accumulation.rate, thickness) were identified based on previous experiences or iteratively after preliminary model inspection. The most common control points for the chronologies are radiocarbon dates (86.1 %), calibrated by the latest calibration curves (IntCal20 and SHcal20 for the terrestrial radiocarbon dates in the northern and southern hemispheres; Marine20 for marine materials). The original literature was consulted when dealing with obvious outliers and inconsistencies. Several major challenges when setting up the chronologies included the waterline issue (18.8 % of records), reservoir effect (4.9 %), and sediment deposition discontinuity (4.4 %). Finally, we numerically compare the LegacyAge 1.0 chronologies to the original ones and show that the chronologies of 95.4 % of records could be improved according to our assessment. Our chronology framework and revised chronologies provide the opportunity to make use of the ages and age uncertainties in synthesis studies of, for example, pollen-based vegetation and climate change. The LegacyAge 1.0 dataset and R code used are open-access and available at PANGAEA (https://doi.pangaea.de/10.1594/PANGAEA.933132) and Github (https://github.com/LongtermEcology/LegacyAge-1.0), respectively.

Description: The current geochronological state of the art for applying the radiocarbon (14C) method to deep-sea sediment archives lacks key information on sediment bioturbation. Here, we apply a sediment accumulation model that simulates the sedimentation and bioturbation of millions of foraminifera, whereby realistic 14C activities (i.e. from a 14C calibration curve) are assigned to each single foraminifera based on its simulation time step. We find that the normal distribution of 14C age typically used to represent discrete-depth sediment intervals (based on the reported laboratory 14C age and measurement error) is unlikely to be a faithful reflection of the actual 14C age distribution for a specific depth interval. We also find that this deviation from the actual 14C age distribution is greatly amplified during the calibration process. Specifically, we find a systematic underestimation of total geochronological error in many cases (by up to thousands of years), as well as the generation of age–depth artefacts in downcore calibrated median age. Even in the case of “perfect” simulated sediment archive scenarios, whereby sediment accumulation rate (SAR), bioturbation depth, reservoir age and species abundance are all kept constant, the 14C measurement and calibration processes generate temporally dynamic median age–depth artefacts on the order of hundreds of years – whereby even high SAR scenarios (40 and 60 cm kyr−1) are susceptible. Such age–depth artefacts can be especially pronounced during periods corresponding to dynamic changes in the Earth's Δ14C history, when single foraminifera of varying 14C activity can be incorporated into single discrete-depth sediment intervals. For certain lower-SAR scenarios, we find that downcore discrete-depth true median age can systematically fall outside the calibrated age range predicted by the 14C measurement and calibration processes, thus leading to systematically inaccurate age estimations. In short, our findings suggest the possibility of 14C-derived age–depth artefacts in the literature. Furthermore, since such age–depth artefacts are likely to coincide with large-scale changes in global Δ14C, which themselves can coincide with large-scale changes in global climate (such as the last deglaciation), 14C-derived age–depth artefacts may have been previously incorrectly attributed to changes in SAR coinciding with global climate. Our study highlights the need for the development of improved deep-sea sediment 14C calibration techniques that include an a priori representation of bioturbation for multi-specimen samples.

Description: Rho.do.mi.cro' bi.um. Gr. neut. n. rhodon the rose; Gr. masc. adj. micros small; Gr. masc. n. bios life; N.L. neut. n. Rhodomicrobium red microbe. Proteobacteria / Alphaproteobacteria / Rhizobiales / Hyphomicrobiaceae / Rhodomicrobium Most characteristic for Rhodomicrobium species is the polar cell growth and the characteristic vegetative growth cycle which includes the formation of peritrichously flagellated swarmer cells and nonmotile “mother cells,” which form prosthecae from one to several times the length of the mother cell. Daughter cells originate as spherical buds at the end of the prosthecae and may undergo differentiation in various ways. They are Gram-negative ovoid to elongate-ovoid bacteria belonging to the Alphaproteobacteria. Internal photosynthetic membranes are of the lamellar type. Photosynthetic pigments are bacteriochlorophyll a and carotenoids of the spirilloxanthin series. The predominant cellular fatty acid is C18:1, which comprises more than 80% of the membrane-bound fatty acids. Ubiquinone and rhodoquinone with 10 isoprene units are present, and the lipopolysaccharides are characterized by a glucosamine-containing, phosphate-free lipid A with amide-bound C16:0 3 OH. DNA G + C content (mol%): 61.8–63.8. Type species: Rhodomicrobium vannielii Duchow and Douglas 1949.

Description: Proteobacteria Alphaproteobacteria Rhizobiales Hyphomicrobiaceae Blas.to.chlo'ris. Gr. masc. n. blastos bud shoot; Gr. masc. adj. chloros green; N.L. fem. n. Blastochloris green bud shoot. Proteobacteria / Alphaproteobacteria / Rhizobiales / Hyphomicrobiaceae / Blastochloris Blastochloris species are anoxygenic phototrophic Alphaproteobacteria that have bacteriochlorophyll b in their photosynthetic reaction centers. Crystals of the photosynthetic reaction centers of Blastochloris viridis were the first that have been studied in high-resolution structure analysis at 3 Å resolution. Internal photosynthetic membranes are present as lamellae underlying and parallel to the cytoplasmic membrane. Cells are rod shaped to ovoid and exhibit polar growth, budding, and asymmetric cell division and form rosette-like cell aggregates. They are motile by means of subpolar flagella and stain Gram-negative. Straight-chain monounsaturated C18:1 is the predominant component of cellular fatty acids. Ubiquinones and menaquinones are present, and the lipopolysaccharides are characterized by a 2,3-diamino-2,3-deoxy-d-glucose (DAG)-containing, phosphate-free lipid A with amide-bound C14:0 3OH. DNA G + C content (mol%): 63.8–68.3. Type species: Blastochloris viridis (Drews and Giesbrecht 1966) Hiraishi 1997 (Rhodopseudomonas viridis Drews and Giesbrecht 1966).

Description: Rho.do.mi.cro' bi.um. Gr. neut. n. rhodon the rose; Gr. masc. adj. micros small; Gr. masc. n. bios life; N.L. neut. n. Rhodomicrobium red microbe. Proteobacteria / Alphaproteobacteria / Rhizobiales / Hyphomicrobiaceae / Rhodomicrobium Most characteristic for Rhodomicrobium species is the polar cell growth and the characteristic vegetative growth cycle which includes the formation of peritrichously flagellated swarmer cells and nonmotile “mother cells,” which form prosthecae from one to several times the length of the mother cell. Daughter cells originate as spherical buds at the end of the prosthecae and may undergo differentiation in various ways. They are Gram‐negative ovoid to elongate‐ovoid bacteria belonging to the Alphaproteobacteria. Internal photosynthetic membranes are of the lamellar type. Photosynthetic pigments are bacteriochlorophyll a and carotenoids of the spirilloxanthin series. The predominant cellular fatty acid is C18:1, which comprises more than 80% of the membrane‐bound fatty acids. Ubiquinone and rhodoquinone with 10 isoprene units are present, and the lipopolysaccharides are characterized by a glucosamine‐containing, phosphate‐free lipid A with amide‐bound C16:0 3 OH. DNA G + C content (mol%): 61.8–63.8. Type species: Rhodomicrobium vannielii Duchow and Douglas 1949.

Description: Geological records show that vast proglacial lakes existed along the land terminating margins of palaeo ice sheets in Europe and North America. Proglacial lakes impact ice sheet dynamics by imposing marine-like boundary conditions at the ice margin. These lacustrine boundary conditions include changes in the ice sheet’s geometry, stress balance and frontal ablation and therefore affect the entire ice sheet’s mass balance. This interaction, however, has not been rigorously implemented in ice sheet models. In this study, the implementation of an adaptive lake boundary into the Parallel Ice Sheet Model (PISM) is described and applied to the glacial retreat of the Laurentide Ice Sheet (LIS). The results show that the presence of proglacial lakes locally enhances the ice flow. Along the continental ice margin, ice streams and ice lobes can be observed. Lacustrine terminating ice streams cause immense thinning of the ice sheet’s interior and thus play a significant role in the demise of the LIS. Due to the presence of lakes, a process similar to the marine ice sheet instability causes the collapse of the ice saddle over Hudson Bay, which blocked drainage via the Hudson Strait. In control experiments without a lake model, Hudson Bay is still glaciated at the end of the simulation. Future studies should target the development of parametrizations that better describe the glacial-lacustrine interactions.

Description: Nitrogen fixers, or diazotrophs, play a key role in the carbon and nitrogen cycle of the world oceans, but the controlling mechanisms are not comprehensively understood yet. The present study compares two paradigms on the ecological niche of diazotrophs in an Earth System Model (ESM). In our standard model configuration, which is representative for most of the state-of-the-art pelagic ecosystem models, diazotrophs take advantage of zooplankton featuring a lower food preference for diazotrophs than for ordinary phytoplankton. We compare this paradigm with the idea that diazotrophs are more competitive under oligotrophic conditions, characterized by low (dissolved, particulate, organic and inorganic) phosphorous availability. Both paradigms are supported by observational evidence and lead to a similar good agreement to the most recent and advanced observation-based nitrogen fixation estimate in our ESM framework. Further, we illustrate that the similarity between the two paradigms breaks in a RCP 8.5 anthropogenic emission scenario. We conclude that a more advanced understanding of the ecological niche of diazotrophs is mandatory for assessing the cycling of essential nutrients, especially under changing environmental conditions. Our results call for more in-situ measurements of cyanobacteria biomass if major controls of nitrogen fixation in the oceans are to be dissected.

Description: The availability of dissolved iron (dFe) exerts an important control on primary production. Recent ocean observation programs have provided information on dFe in many parts of the ocean, but knowledge is still limited concerning the rates of processes that control the concentrations and cycling of dFe in the ocean and hence the role of dFe as a determinant of global primary production. We constructed a three-dimensional gridded dataset of oceanic dFe concentrations by using both observations and a simple model of the iron cycle, and estimated the difference of processes among the ocean basins in controlling the dFe distributions. A Green's function approach was used to integrate the observations and the model. The reproduced three-dimensional dFe distribution indicated that iron influx from aeolian dust and from shelf sediment were 7.6 Gmol yr and 4.4 Gmol yr in the Atlantic Ocean and 0.4 Gmol yr and 4.1 Gmol yr in the Pacific Ocean. The residence times were estimated to be 12.2 years in the Atlantic and 80.4 years in the Pacific. These estimates imply large differences in the cycling of dFe between the two ocean basins that would need to be taken into consideration when projecting future iron biogeochemical cycling under different climate change scenarios. Although there is some uncertainty in our estimates, global estimates of iron cycle characteristics based on this approach can be expected to enhance our understanding of the material cycle and hence of the current and future rates of marine primary production.

Description: The distribution of the main water masses in the Atlantic Ocean are investigated with the Optimal Multi-Parameter (OMP) method. The properties of the main water masses in the Atlantic Ocean are described in a companion article; here these definitions are used to map out the general distribution of those water masses. Six key properties, including conservative (potential temperature and salinity) and non-conservative (oxygen, silicate, phosphate and nitrate), are incorporated into the OMP analysis to determine the contribution of the water masses in the Atlantic Ocean based on the GLODAP v2 observational data. To facilitate the analysis the Atlantic Ocean is divided into four vertical layers based on potential density. Due to the high seasonal variability in the mixed layer, this layer is excluded from the analysis. Central waters are the main water masses in the upper/central layer, generally featuring high potential temperature and salinity and low nutrient concentrations and are easily distinguished from the intermediate water masses. In the intermediate layer, the Antarctic Intermediate Water (AAIW) from the south can be detected to ~30°N, whereas the Subarctic Intermediate Water (SAIW), having similarly low salinity to the AAIW flows from the north. Mediterranean Overflow Water (MOW) flows from the Strait of Gibraltar as a high salinity water. NADW dominates the deep and overflow layer both in the North and South Atlantic. In the bottom layer, AABW is the only natural water mass with high silicate signature spreading from the Antarctic to the North Atlantic. Due to the change of water mass properties, in this work we renamed to North East Antarctic Bottom Water NEABW north of the equator. Similarly, the distributions of Labrador Sea Water (LSW), Iceland Scotland Overflow Water (ISOW), and Denmark Strait Overflow Water (DSOW) forms upper and lower portion of NADW, respectively roughly south of the Grand Banks between ~50 and 66°N. In the far south the distributions of Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW) are of significance to understand the formation of the AABW.

Description: The northeast Atlantic encompasses archetypal examples of volcanic rifted margins. Twenty-five years after the last ODP (Ocean Drilling Program) leg on these volcanic margins, the reasons for excess melting are still disputed with at least three competing hypotheses being discussed. We are proposing a new drilling campaign that will constrain the timing, rates of volcanism, and vertical movements of rifted margins. This will allow us to parameterise geodynamic models that can distinguish between the hypotheses. Furthermore, the drilling-derived data will help us to understand the role of breakup magmatism as a potential driver for the Palaeocene–Eocene thermal maximum (PETM) and its influence on the oceanographic circulation in the earliest phase of the northeast Atlantic Ocean formation. Tackling these questions with a new drilling campaign in the northeast Atlantic region will advance our understanding of the long-term interactions between tectonics, volcanism, oceanography, and climate and the functioning of subpolar northern ecosystems and climate during intervals of extreme warmth.

Description: Recent surveys of marine microbial diversity have identified a previously unrecognized lineage of diplonemid protists as being among the most diverse heterotrophic eukaryotes in global oceans. Despite their monophyly (and assumed importance), they lack a formal taxonomic description, and are informally known as deep-sea pelagic diplonemids (DSPDs) or marine diplonemids. Recently, we documented morphology and molecular sequences from several DSPDs, one of which is particularly widespread and abundant in environmental sequence data. To simplify the communication of future work on this important group, here we formally propose to erect the family Eupelagonemidae to encompass this clade, as well as a formal genus and species description for the apparently most abundant phylotype, Eupelagonema oceanica, for which morphological information and single-cell amplified genome data are currently available. © 2018 International Society of Protistologists

Description: Spores of the dinoflagellate Chytriodinium are known to infest copepod eggs causing their lethality. Despite the potential to control the population of such an ecologically important host, knowledge about Chytriodinium parasites is limited: we know little about phylogeny, parasitism, abundance, or geographical distribution. We carried out genome sequence surveys on four manually isolated sporocytes from the same sporangium, which seemed to be attached to a copepod nauplius, to analyze the phylogenetic position of Chytriodinium based on SSU and concatenated SSU/LSU rRNA gene sequences, and also characterize two genes related to the plastidial heme pathway, hemL and hemY. The results suggest the presence of a cryptic plastid in Chytriodinium and a photosynthetic ancestral state of the parasitic Chytriodinium/Dissodinium clade. Finally, by mapping Tara Oceans V9 SSU amplicon data to the recovered SSU rRNA gene sequences from the sporocytes, we show that globally, Chytriodinium parasites are most abundant within the pico/nano- and mesoplankton of the surface ocean and almost absent within microplankton, a distribution indicating that they generally exist either as free-living spores or host-associated sporangia. © 2018 International Society of Protistologists

Description: The El Niño Southern Oscillation (ENSO) with its warm (El Niño) and cold (La Niña) phase has strong impacts on marine ecosystems off Peru. This influence extends from changes in nutrient availability to productivity and oxygen levels. While several studies have demonstrated the influence of ENSO events on biological productivity, less is known about their impact on oxygen concentrations. In situ observations along the Peruvian and Chilean coast have shown a strong water column oxygenation during the 1997/1998 strong El Niño event. These observations suggest a deepening of the oxygen minimum zone (OMZ) along the continental shelf. However, due to reduced spatial coverage of the existing in situ observations, no studies have yet demonstrated the OMZ response to El Niño events in the whole Eastern Tropical South Pacific (ETSP). Furthermore, most studies have focused on El Niño events. Much less attention was given to the oxygen dynamics under La Niña influence. Here, we provide a comprehensive analysis of the ENSO influence on OMZ dynamics. Interannual variability of the OMZ during the period 1990–2010 is derived from a regional coupled physical-biogeochemical model forced with realistic atmospheric and lateral boundary conditions. Our results show a reduction of the vertical extent and a deepening of suboxic waters (SW) during the El Niño phase. During the La Niña phase, there is a vertical expansion of SW. These fluctuations in OMZ extent are due to changes in oxygen supply into its core depth mainly from lateral margins. During the El Niño phase, the enhanced lateral oxygen supply from the subtropics is the main reason for the reduction of SW in both coastal and offshore regions. During the La Niña phase, the oxygenated subtropical waters are blocked by the poleward transport along the southern margin of the OMZ. Consequently, oxygen concentrations within the OMZ are reduced and suboxic conditions expand during La Niña. The detailed analysis of transport pathways presented here provides new insights into how ENSO variability affects the oxygen-sensitive marine biogeochemistry of the ETSP.

Description: Oxygen minimum zones (OMZs) in the open ocean occur below the surface in regions of weak ventilation and high biological productivity. Very low levels of dissolved oxygen affect marine life and alter biogeochemical cycles. One of the most intense but least understood OMZs in the world is located in the Arabian Sea in a depth range between 300 to 1000 m. Within the last decades observations suggest a decreasing oxygen trend. Thus, an improved understanding of the crucial processes is necessary for a reliable assessment of the future development of the Arabian Sea OMZ. This study uses a combination of observational data as well as reanalysis velocity fields from the ocean model Hycom (Hybrid Coordinate Ocean Model) to explore the ventilation dynamics of the Arabian Sea OMZ. Our results show that the OMZ features a strong seasonal cycle with regional differences that is correlated with the monsoon system: In the eastern basin, the OMZ is strongest during the winter monsoon with a core thickness of 1000 m depth and oxygen values of less than 5 µmol/kg. Ventilation during that phase is dominated by Persian Gulf water, that clockwise circles the perimeter of the basin and enters the OMZ from the north. During the summer monsoon ventilation from the southeast leads to higher oxygen values indicating a reverse flow along the Indian coast in the intermediate layer compared to the southeastward surface currents. The seasonal cycle in the western basin has the same seasonality as the one in the eastern basin with a core thickness of 900 m during the winter monsoon. The oxygen supply during the summer monsoon is weaker compared to the eastern basin and correlates with the ventilation of Persian Gulf (Red Sea) water during the summer monsoon (autumn inter-monsoon) phase. As the interior exchange between the eastern and western basin is weak, the more pronounced OMZ in the eastern basin is explained by prolonged ventilation time scales. For the eastern (western) basin Persian Gulf water needs 2–3 (1–2) years and Red Sea water 7–8 (3–4) years to ventilate the OMZ.

Description: Ice sheet numerical modeling is an important tool to estimate the dynamic contribution of the Antarctic ice sheet to sea level rise over the coming centuries. The influence of initial conditions on ice sheet model simulations, however, is still unclear. To better understand this influence, an initial state intercomparison exercise (initMIP) has been developed to compare, evaluate, and improve initialization procedures and estimate their impact on century-scale simulations. initMIP is the first set of experiments of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), which is the primary Coupled Model Intercomparison Project Phase 6 (CMIP6) activity focusing on the Greenland and Antarctic ice sheets. Following initMIP-Greenland, initMIP-Antarctica has been designed to explore uncertainties associated with model initialization and spin-up and to evaluate the impact of changes in external forcings. Starting from the state of the Antarctic ice sheet at the end of the initialization procedure, three forward experiments are each run for 100 years: a control run, a run with a surface mass balance anomaly, and a run with a basal melting anomaly beneath floating ice. This study presents the results of initMIP-Antarctica from 25 simulations performed by 16 international modeling groups. The submitted results use different initial conditions and initialization methods, as well as ice flow model parameters and reference external forcings. We find a good agreement among model responses to the surface mass balance anomaly but large variations in responses to the basal melting anomaly. These variations can be attributed to differences in the extent of ice shelves and their upstream tributaries, the numerical treatment of grounding line, and the initial ocean conditions applied, suggesting that ongoing efforts to better represent ice shelves in continental-scale models should continue.

Description: We present here the first results, for the preindustrial and mid-Holocene climatological periods, of the newly developed isotope-enhanced version of the fully coupled Earth system model MPI-ESM, called hereafter MPI-ESM-wiso. The water stable isotopes H162O, H182O and HDO have been implemented into all components of the coupled model setup. The mid-Holocene provides the opportunity to evaluate the model response to changes in the seasonal and latitudinal distribution of insolation induced by different orbital forcing conditions. The results of our equilibrium simulations allow us to evaluate the performance of the isotopic model in simulating the spatial and temporal variations of water isotopes in the different compartments of the hydrological system for warm climates. For the preindustrial climate, MPI-ESM-wiso reproduces very well the observed spatial distribution of the isotopic content in precipitation linked to the spatial variations in temperature and precipitation rate. We also find a good model–data agreement with the observed distribution of isotopic composition in surface seawater but a bias with the presence of surface seawater that is too 18O-depleted in the Arctic Ocean. All these results are improved compared to the previous model version ECHAM5/MPIOM. The spatial relationships of water isotopic composition with temperature, precipitation rate and salinity are consistent with observational data. For the preindustrial climate, the interannual relationships of water isotopes with temperature and salinity are globally lower than the spatial ones, consistent with previous studies. Simulated results under mid-Holocene conditions are in fair agreement with the isotopic measurements from ice cores and continental speleothems. MPI-ESM-wiso simulates a decrease in the isotopic composition of precipitation from North Africa to the Tibetan Plateau via India due to the enhanced monsoons during the mid-Holocene. Over Greenland, our simulation indicates a higher isotopic composition of precipitation linked to higher summer temperature and a reduction in sea ice, shown by positive isotope–temperature gradient. For the Antarctic continent, the model simulates lower isotopic values over the East Antarctic plateau, linked to the lower temperatures during the mid-Holocene period, while similar or higher isotopic values are modeled over the rest of the continent. While variations of isotopic contents in precipitation over West Antarctica between mid-Holocene and preindustrial periods are partly controlled by changes in temperature, the transport of relatively 18O-rich water vapor near the coast to the western ice core sites could play a role in the final isotopic composition. So, more caution has to be taken about the reconstruction of past temperature variations during warm periods over this area. The coupling of such a model with an ice sheet model or the use of a zoomed grid centered on this region could help to better describe the role of the water vapor transport and sea ice around West Antarctica. The reconstruction of past salinity through isotopic content in sea surface waters can be complicated for regions with strong ocean dynamics, variations in sea ice regimes or significant changes in freshwater budget, giving an extremely variable relationship between the isotopic content and salinity of ocean surface waters over small spatial scales. These complicating factors demonstrate the complexity of interpreting water isotopes as past climate signals of warm periods like the mid-Holocene. A systematic isotope model intercomparison study for further insights on the model dependency of these results would be beneficial.

Description: Probabilistic spatial reconstructions of past climate states are valuable to quantitatively study the climate system under different forcing conditions because they combine the information contained in a proxy synthesis into a comprehensible product. Unfortunately, they are subject to a complex uncertainty structure due to complicated proxy–climate relations and sparse data, which makes interpolation between samples difficult. Bayesian hierarchical models feature promising properties to handle these issues, like the possibility to include multiple sources of information and to quantify uncertainties in a statistically rigorous way. We present a Bayesian framework that combines a network of pollen and macrofossil samples with a spatial prior distribution estimated from a multi-model ensemble of climate simulations. The use of climate simulation output aims at a physically reasonable spatial interpolation of proxy data on a regional scale. To transfer the pollen data into (local) climate information, we invert a forward version of the probabilistic indicator taxa model. The Bayesian inference is performed using Markov chain Monte Carlo methods following a Metropolis-within-Gibbs strategy. Different ways to incorporate the climate simulations into the Bayesian framework are compared using identical twin and cross-validation experiments. Then, we reconstruct the mean temperature of the warmest and mean temperature of the coldest month during the mid-Holocene in Europe using a published pollen and macrofossil synthesis in combination with the Paleoclimate Modelling Intercomparison Project Phase III mid-Holocene ensemble. The output of our Bayesian model is a spatially distributed probability distribution that facilitates quantitative analyses that account for uncertainties.

Description: Heteroplasmy occurs when copies of an organellar genome (plastid or mitochondrial) differ from one another either within a cell or among cells within an individual. This phenomenon was first discovered in plastids over 100 years ago, though ‘heteroplasmy’ was not formally defined until decades later. Mitochondrial and plastid heteroplasmy have since been discovered in diverse taxa, including numerous plants, particularly those with the gynodioecious breeding system. Though heteroplasmy can arise through mutations in organellar genomes, biparental inheritance of organelles often generates heteroplasmy. This article is intended to summarise the cytoploid nature of organellar genomes and different aspects of mitochondrial and plastid heteroplasmy, from its discovery, to the development of detection methods. We will also discuss the effects of heteroplasmy on individuals, populations, and species, with regard to fitness, cytonuclear interactions, and genome evolution. Finally, we highlight a few research questions which we consider in need of further investigation to understand the prevalence and effects of heteroplasmy in natural settings.

Description: Large calderas are among the Earth's major volcanic features. They are associated with large magma reservoirs and elevated geothermal gradients. Caldera-forming eruptions result from the withdrawal and collapse of the magma chambers and produce large-volume pyroclastic deposits and later-stage deformation related to post-caldera resurgence and volcanism. Unrest episodes are not always followed by an eruption; however, every eruption is preceded by unrest. The Campi Flegrei caldera (CFc), located along the eastern Tyrrhenian coastline in southern Italy, is close to the densely populated area of Naples. It is one of the most dangerous volcanoes on Earth and represents a key example of an active, resurgent caldera. It has been traditionally interpreted as a nested caldera formed by collapses during the 100–200 km3 Campanian Ignimbrite (CI) eruption at ∼39 ka and the 40 km3 eruption of the Neapolitan Yellow Tuff (NYT) at ∼15 ka. Recent studies have suggested that the CI may instead have been fed by a fissure eruption from the Campanian Plain, north of Campi Flegrei. A MagellanPlus workshop was held in Naples, Italy, on 25–28 February 2017 to explore the potential of the CFc as target for an amphibious drilling project within the International Ocean Discovery Program (IODP) and the International Continental Drilling Program (ICDP). It was agreed that Campi Flegrei is an ideal site to investigate the mechanisms of caldera formation and associated post-caldera dynamics and to analyze the still poorly understood interplay between hydrothermal and magmatic processes. A coordinated onshore–offshore drilling strategy has been developed to reconstruct the structure and evolution of Campi Flegrei and to investigate volcanic precursors by examining (a) the succession of volcanic and hydrothermal products and related processes, (b) the inner structure of the caldera resurgence, (c) the physical, chemical, and biological characteristics of the hydrothermal system and offshore sediments, and (d) the geological expression of the phreatic and hydromagmatic eruptions, hydrothermal degassing, sedimentary structures, and other records of these phenomena. The deployment of a multiparametric in situ monitoring system at depth will enable near-real-time tracking of changes in the magma reservoir and hydrothermal system.

Description: The international endeavour to retrieve a continuous ice core, which spans the middle Pleistocene climate transition ca. 1.2–0.9 Myr ago, encompasses a multitude of field and model-based pre-site surveys. We expand on the current efforts to locate a suitable drilling site for the oldest Antarctic ice core by means of 3-D continental ice-sheet modelling. To this end, we present an ensemble of ice-sheet simulations spanning the last 2 Myr, employing transient boundary conditions derived from climate modelling and climate proxy records. We discuss the imprint of changing climate conditions, sea level and geothermal heat flux on the ice thickness, and basal conditions around previously identified sites with continuous records of old ice. Our modelling results show a range of configurational ice-sheet changes across the middle Pleistocene transition, suggesting a potential shift of the West Antarctic Ice Sheet to a marine-based configuration. Despite the middle Pleistocene climate reorganisation and associated ice-dynamic changes, we identify several regions conducive to conditions maintaining 1.5 Myr (million years) old ice, particularly around Dome Fuji, Dome C and Ridge B, which is in agreement with previous studies. This finding strengthens the notion that continuous records with such old ice do exist in previously identified regions, while we are also providing a dynamic continental ice-sheet context.

Description: While nonlinear stochastic partial differential equations arise naturally in spatiotemporal modeling, inference for such systems often faces two major challenges: sparse noisy data and ill-posedness of the inverse problem of parameter estimation. To overcome the challenges, we introduce a strongly regularized posterior by normalizing the likelihood and by imposing physical constraints through priors of the parameters and states. We investigate joint parameter-state estimation by the regularized posterior in a physically motivated nonlinear stochastic energy balance model (SEBM) for paleoclimate reconstruction. The high-dimensional posterior is sampled by a particle Gibbs sampler that combines a Markov chain Monte Carlo (MCMC) method with an optimal particle filter exploiting the structure of the SEBM. In tests using either Gaussian or uniform priors based on the physical range of parameters, the regularized posteriors overcome the ill-posedness and lead to samples within physical ranges, quantifying the uncertainty in estimation. Due to the ill-posedness and the regularization, the posterior of parameters presents a relatively large uncertainty, and consequently, the maximum of the posterior, which is the minimizer in a variational approach, can have a large variation. In contrast, the posterior of states generally concentrates near the truth, substantially filtering out observation noise and reducing uncertainty in the unconstrained SEBM.

Description: We present a software toolbox that allows the efficient collection, management and maintenance of larger paleoceanographic data sets. The program combines a graphical user interface (GUI) with a simple document-based database and functionality for visualization, stratigraphy (visual alignment and radiocarbon calibration), age modelling and efficient ensemble time-series generation to create larger homogenous data compilations. Data can be imported from Excel or text files, are stored locally in netCDF format and can be easily exchanged between collaborating scientists. Within a data collection, data can be imported either to proxy-specific sub-collections or to a multi-proxy (“miscellaneous”) sub-collection that allows the import and management of any downcore data. A single age model is shared among all proxies of a core within a collection. The stand-alone software can be used with Windows and macOS and does not require web access. Installers of the current version for both Windows 10 and macOS including the C++ code can be downloaded from https://www.marum.de/Stefan-Mulitza/PaleoDataView.html (last access: 5 December 2019) along with a detailed user guide.

Description: Combining ocean general circulation models with proxy data via data assimilation is a means to obtain estimates of past ocean states that are consistent with model physics as well as with proxy data. The climate during the Last Glacial Maximum (LGM, 19–23 ka) was substantially different from today. Even though boundary conditions are comparatively well known, the large-scale patterns of the ocean circulation during this time remain uncertain. Previous efforts to combine ocean models with proxy data have shown dissimilar results regarding the state of the ocean, in particular of the Atlantic Meridional Overturning Circulation. Here, we present a new LGM ocean state estimate that extents previous estimates by using global benthic as well as planktic data on the oxygen isotopic composition of calcite. It is further constrained by global seasonal and annual sea surface temperature (SST) reconstructions. The estimate shows an Atlantic Ocean that is similar to the Late Holocene Atlantic Ocean but with a reduced formation of Antarctic Bottom Water, in contrast to results of previous studies. The results indicate that SST and oxygen isotopic data alone do not require the presence of a shallower North Atlantic Deep Water and a more extensive Antarctic Bottom Water, and highlight the need for more proxy data of different types to obtain reliable ocean state estimates. Additional adjoint sensitivity experiments reveal that data from the deep North Atlantic and from the global deep Southern Ocean are most important to constrain the Atlantic Meridional Overturning Circulation.

Description: The species composition of many groups of marine plankton appears well predicted by sea surface temperature (SST). Consequently, fossil plankton assemblages have been widely used to reconstruct past SST. Most applications of this approach make use of the highest possible taxonomic resolution. However, not all species are sensitive to temperature, and their distribution may be governed by other parameters. There are thus reasons to question the merit of including information about all species, both for transfer function performance and for its effect on reconstructions. Here we investigate the effect of species selection on planktonic foraminifera transfer functions. We assess species importance for transfer function models using a random forest technique and evaluate the performance of models with an increasing number of species. Irrespective of using models that use the entire training set (weighted averaging) or models that use only a subset of the training set (modern analogue technique), we find that the majority of foraminifera species does not carry useful information for temperature reconstruction. Less than one-third of the species in the training set is required to provide a temperature estimate with a prediction error comparable to a transfer function that uses all species in the training set. However, species selection matters for paleotemperature estimates. We find that transfer function models with a different number of species but with the same error may yield different reconstructions of sea surface temperature when applied to the same fossil assemblages. This ambiguity in the reconstructions implies that fossil assemblage change reflects a combination of temperature and other environmental factors. The contribution of the additional factors is site and time specific, indicating ecological and geological complexity in the formation of the sedimentary assemblages. The possibility of obtaining multiple different reconstructions from a single sediment record presents a previously unrecognized source of uncertainty for sea surface temperature estimates based on planktonic foraminifera assemblages. This uncertainty can be evaluated by determining the sensitivity of the reconstructions to species pruning.

Description: Although narrow‐azimuth towed‐streamer data provides good image quality for structural interpretation, it is generally accepted that for wide‐azimuth marine surveys seabed receivers deliver superior seismic reflection measurements and seismically derived reservoir attributes. However, seabed surveys are not widely used due to the higher acquisition costs when compared to streamer acquisition. In recent years, there have been significant engineering efforts to automate receiver deployment and retrieval in order to minimize the cost differential and conduct cost‐efficient seabed receiver seismic surveys. These engineering efforts include industrially engineered nodes, nodes‐on‐a‐rope deployment schemes and even robotic nodes, which swim to and from the deployment location. This move to automation is inevitable, leading to robotization of seismic data acquisition for exploration and development activities in the oil and gas industry. We are developing a robotic‐based technology, which utilizes autonomous underwater vehicles as seismic sensors without the need of using a remotely operated vehicle for deployment and retrieval. In this paper, we describe the autonomous underwater vehicle evolution throughout the project years from initial heavy and bulky nodes to fully autonomous light and flexible underwater receivers. Results obtained from two field pilot tests using different generations of autonomous underwater vehicles indicate that the seismic coupling, and navigation based on underwater acoustics are very reliable and robust.

Description: Regional climate modeling bridges the gap between the coarse resolution of current global climate models and the regional-to-local scales, where the impacts of climate change are of primary interest. Here, we present a review of the added value of the regional climate modeling approach within the scope of paleoclimate research and discuss the current major challenges and perspectives. Two time periods serve as an example: the Holocene, including the Last Millennium, and the Last Glacial Maximum. Reviewing the existing literature reveals the benefits of regional paleo climate modeling, particularly over areas with complex terrain. However, this depends largely on the variable of interest, as the added value of regional modeling arises from a more realistic representation of physical processes and climate feedbacks compared to global climate models, and this affects different climate variables in various ways. In particular, hydrological processes have been shown to be better represented in regional models, and they can deliver more realistic meteorological data to drive ice sheet and glacier modeling. Thus, regional climate models provide a clear benefit to answer fundamental paleoclimate research questions and may be key to advance a meaningful joint interpretation of climate model and proxy data.

Description: A marine seismic method based on continuous source and receiver wavefields has been developed. The method requires continuous recording of the seismic data. The source that may consist of multiple source elements can emit signals continuously while moving. The ideal source wavefield to be used with this method should be as white as possible both in a temporal and a spatial sense to avoid deep notches in the spectrum enabling a stable multi‐dimensional deconvolution. White noise has such properties. However, equipment that can generate white noise does not exist. In order to generate a continuous source wavefield that is approaching the properties of white noise using existing equipment onboard marine seismic vessels, individual air‐guns can be triggered with short randomized time intervals in a near‐continuous fashion. The main potential benefits with the method are to reduce the environmental impact of marine seismic surveys and to improve acquisition efficiency. The peak sound pressure levels are significantly reduced by triggering one air‐gun at a time compared to conventional marine seismic sources. Sound exposure levels are also reduced in most directions. Since the method is based on continuous recording of seismic data and the air‐guns are triggered based on time and not based on position, there are less vessel speed limitations compared to conventional marine seismic data acquisition. Also, because the source wavefield is spread out in time, the wavefields emitted from source elements in different cross‐line positions can be designed such that the emitted wavefield is spatially white in this direction. This means that source elements in multiple cross‐line positions can be operated simultaneously, potentially improving the cross‐line sampling and/or the acquisition efficiency.

Description: Basalt weathering is one of many relevant processes balancing the global carbon cycle via land–ocean alkalinity fluxes. The CO2 consumption by weathering can be calculated using alkalinity and is often scaled with runoff and/or temperature. Here, it is tested if the surface age distribution of a volcanic system derived by geological maps is a useful proxy for changes in alkalinity production with time. A linear relationship between temperature normalized alkalinity fluxes and the Holocene area fraction of a volcanic field was identified using information from 33 basalt volcanic fields, with an r2=0.93. This relationship is interpreted as an aging function and suggests that fluxes from Holocene areas are ∼10 times higher than those from old inactive volcanic fields. However, the cause for the decrease with time is probably a combination of effects, including a decrease in alkalinity production from material in the shallow critical zone as well as a decline in hydrothermal activity and magmatic CO2 contribution. The addition of fresh reactive material on top of the critical zone has an effect in young active volcanic settings which should be accounted for, too. A comparison with global models suggests that global alkalinity fluxes considering Holocene basalt areas are ∼60 % higher than the average from these models imply. The contribution of Holocene areas to the global basalt alkalinity fluxes is today however only ∼5 %, because identified, mapped Holocene basalt areas cover only ∼1 % of the existing basalt areas. The large trap basalt proportion on the global basalt areas today reduces the relevance of the aging effect. However, the aging effect might be a relevant process during periods of globally intensive volcanic activity, which remains to be tested.

Description: Dynamic vegetation models simulate global vegetation in terms of fractional coverage of a few plant functional types (PFTs). Although these models often share the same concept, they differ with respect to the number and kind of PFTs, complicating the comparability of simulated vegetation distributions. Pollen-based vegetation reconstructions are initially only available in the form of time series of individual taxa that are not distinguished in the models. Thus, to evaluate simulated vegetation distributions, the modelling results and pollen-based vegetation reconstructions have to be converted into a comparable format. The classical approach is the method of biomisation, but hitherto PFT-based biomisation methods were only available for individual models. We introduce and evaluate a simple, universally applicable technique to harmonise PFT distributions by assigning them into nine mega-biomes, using only assumptions on the minimum PFT cover fractions and few bioclimatic constraints (based on the 2 m temperature). These constraints mainly follow the limitation rules used in the classical biome models (here BIOME4). We test the method for six state-of-the-art dynamic vegetation models that are included in Earth system models based on pre-industrial, mid-Holocene and Last Glacial Maximum simulations. The method works well, independent of the spatial resolution or the complexity of the models. Large biome belts (such as tropical forest) are generally better represented than regionally confined biomes (warm–temperate forest, savanna). The comparison with biome distributions inferred via the classical biomisation approach of forcing biome models (here BIOME1) with the simulated climate states shows that the PFT-based biomisation is even able to keep up with the classical method. However, as the new method considers the PFT distributions actually calculated by the Earth system models, it allows for a direct comparison and evaluation of simulated vegetation distributions which the classical method cannot do. Thereby, the new method provides a powerful tool for the evaluation of Earth system models in general.

Description: The sedimentary stable nitrogen isotope compositions of bulk organic matter (δ15Nbulk) and silicon isotope composition of diatoms (δ30SiBSi) both mainly reflect the degree of past nutrient utilization by primary producers. However, in ocean areas where anoxic and suboxic conditions prevail, the δ15Nbulk signal ultimately recorded within the sediments is also influenced by water column denitrification causing an increase in the subsurface δ15N signature of dissolved nitrate (δ15NO3−) upwelled to the surface. Such conditions are found in the oxygen minimum zone off Peru, where at present an increase in subsurface δ15NO3− from North to South along the shelf is observed due to ongoing denitrification within the pole-ward flowing subsurface waters, while the δ30Si signature of silicic acid (δ30Si(OH)4) at the same time remains unchanged. Here, we present three new δ30SiBSi records between 11° S and 15° S and compare these to previously published δ30SiBSi and δ15Nbulk records from Peru covering the past 600 years. We present a new approach to calculate past subsurface δ15NO3− signatures based on the correlation of δ30SiBSi and δ15Nbulk signatures at a latitudinal resolution for different time periods. Our results show source water δ15NO3− compositions during the last 200 years, the Current Warm Period (CWP) and during short-term arid events prior to that, which are close to modern values increasing southward from 7 to 10 ‰ (between 11° S and 15° S). In contrast, humid conditions during the Little Ice Age (LIA) reflect consistently low δ15NO3− values between 6 and 7.5‰. Furthermore, we are able to relate the short-term variability in both isotope compositions to changes in the ratio of nutrients (NO3− : Si(OH)4) taken up by different dominating phytoplankton groups (diatoms and non-siliceous phytoplankton) under the variable climatic conditions of the past 600 years.

Description: The open ocean is a major source of nitrous oxide (N2O), an atmospheric trace gas attributable to global warming and ozone depletion. Intense sea-to-air N2O fluxes occur in major oceanic upwelling regions such as the eastern tropical South Pacific (ETSP). The ETSP is influenced by the El Niño–Southern Oscillation that leads to inter-annual variations in physical, chemical, and biological properties in the water column. In October 2015, a strong El Niño event was developing in the ETSP; we conduct field observations to investigate (1) the N2O production pathways and associated biogeochemical properties and (2) the effects of El Niño on water column N2O distributions and fluxes using data from previous non-El Niño years. Analysis of N2O natural abundance isotopomers suggested that nitrification and partial denitrification (nitrate and nitrite reduction to N2O) were occurring in the near-surface waters; indicating that both pathways contributed to N2O effluxes. Higher-than-normal sea surface temperatures were associated with a deepening of the oxycline and the oxygen minimum layer. Within the shelf region, surface N2O supersaturation was nearly an order of magnitude lower than that of non-El Niño years. Therefore, a significant reduction of N2O efflux (75 %–95 %) in the ETSP occurred during the 2015 El Niño. At both offshore and coastal stations, the N2O concentration profiles during El Niño showed moderate N2O concentration gradients, and the peak N2O concentrations occurred at deeper depths during El Niño years; this was likely the result of suppressed upwelling retaining N2O in subsurface waters. At multiple stations, water-column inventories of N2O within the top 1000 m were up to 160 % higher than those measured in non-El Niño years, indicating that subsurface N2O during El Niño could be a reservoir for intense N2O effluxes when normal upwelling is resumed after El Niño.

Description: We investigate the role of the tropics, the stratosphere, and atmosphere‐ocean coupling for seasonal forecasts of strong, potentially damaging, Northern Hemisphere extratropical winter wind storm frequencies. This is done by means of relaxation experiments with the European Centre for Medium‐Range Weather Forecasts model, which allow us to prescribe perfect forecasts for specific parts of the coupled atmosphere‐ocean system. We find that perfect predictions of the Northern Hemisphere stratosphere significantly enhance winter storm predictive skill between eastern Greenland and Northern Europe. Correct seasonal predictions of the occurrence of stratospheric sudden warmings play a decisive role. The importance of correctly predicting the tropics and of two‐way atmosphere‐ocean coupling, both for forecasting stratospheric sudden warming risk and, correspondingly, severe winter storm frequency, is noted.

Description: The early Eocene (56 to 48 million years ago) is inferred to have been the most recent time that Earth's atmospheric CO2 concentrations exceeded 1000 ppm. Global mean temperatures were also substantially warmer than present day. As such, study of early Eocene climate provides insight into how a super-warm Earth system behaves and offers an opportunity to 10 evaluate climate models under conditions of high greenhouse gas forcing. The Deep Time Model Intercomparison Project (DeepMIP) is a systematic model-model and model-data intercomparison of three early Paleogene time slices: latest Paleocene, Paleocene-Eocene thermal maximum and early Eocene climatic optimum. A previous article outlined the model experimental design for climate model simulations. In this article, we outline the methodologies to be used for the compilation and analysis of climate proxy data, primarily proxies for temperature and CO2. This paper establishes the protocols for a concerted and 15 coordinated effort to compile the climate proxy records across a wide geographic range. The resulting climate "atlas" will be used to constrain and evaluate climate models for the three selected time intervals, and provide insights into the mechanisms that control these warm climate states. We provide version 0.1 of this database, in anticipation that this will be expanded in subsequent publications.

Description: The northern part of the South China Sea is characterized by widespread occurrence of bottom simulating reflectors (BSR) indicating the presence of marine gas hydrate. Because the area covers both a tectonically inactive passive margin and the termination of a subduction zone, the influence of tectonism on the dynamics of gas hydrate systems can be studied in this region. Geophysical data show that there are multiple thrust faults on the active margin while much fewer and smaller faults exist in the passive margin. This tectonic difference matches with a difference in the geophysical characteristics of the gas hydrate systems. High hydrate saturation derived from ocean bottom seismometer data and controlled source electromagnetic data and conspicuous high‐amplitude reflections in P‐Cable 3D seismic data above the BSR are found in the anticlinal ridges of the active margin. In contrast all geophysical evidence for the passive margin points to normal to low hydrate saturations. Geochemical analyses of gas samples collected at seep sites on the active margin show methane with heavy δ13C isotope composition, while gas collected at the passive margin shows light carbon isotope composition. Thus, we interpret the passive margin as a typical gas hydrate province fuelled by biogenic production of methane and the active margin gas hydrate system as a system that is fuelled not only by biogenic gas production but also by additional advection of thermogenic methane from the subduction system.

Description: The mechanisms controlling the variability of oxygen levels in the ocean are poorly quantified. We focus here on the impact of wind synoptic variability associated with tropical convective regions and extra‐tropical storms. Removing the wind higher frequencies of variability (2 days – 1 month) in an atmosphere reanalysis used to force an ocean model decreases wind stress by up to 20% in the tropics and 50% in the mid‐latitudes, weakening wind‐driven ocean circulation by 20%. Oxygen levels decrease by up to 10 mmol.m‐3 in tropical oceans and 30 mmol.m‐3 in subtropical gyres mainly due to changes in advective processes. While a large part of the tropical oxygen anomaly has local origins, changes in oxygen levels in the subtropical gyres modulate tropical oxygen distribution. Our study suggests that the “storminess” of the ocean is an important parameter that could determine the future evolution of poorly oxygenated regions.

Description: The Benguela Upwelling system (BUS) is the most productive of all eastern boundary upwelling ecosystems and it hosts a well‐developed oxygen minimum zone. As such, the BUS is a potential hotspot for production of N2O, a potent greenhouse gas derived from microbially‐driven decay of sinking organic matter. Yet, the extent at which near‐surface waters emit N2O to the atmosphere in the BUS is highly uncertain. Here we present the first high‐resolution surface measurements of N2O across the northern part of the BUS (nBUS). We found strong gradients with a three‐fold increase in N2O concentrations near the coast as compared with open ocean waters. Our observations show enhanced sea‐to‐air fluxes of N2O (up to 1.67 nmol m−2 s−1) in association with local upwelling cells. Based on our data we suggest that the nBUS can account for 13% of the total coastal upwelling source of N2O to the atmosphere.

Description: Hydroxylamine (NH 2 OH), a short-lived intermediate in the nitrogen cycle, is a potential precursor of nitrous oxide (N 2 O) in the ocean. However, measurements of NH 2 OH in the ocean are sparse. Here we present a data set of depth profiles of NH 2 OH from the equatorial Atlantic Ocean and the eastern tropical South Pacific and compare it to N 2 O, nitrate, and nitrite profiles under varying oxygen conditions. The presence of NH 2 OH in surface waters points toward surface nitrification in the upper 100 m. Overall, we found a ratio of 1:3 between NH 2 OH and N 2 O in open ocean areas when oxygen concentrations were 〉50 μmol/L. In the equatorial Atlantic Ocean and the open ocean eastern tropical South Pacific, where nitrification is the dominant N 2 O production pathway, stepwise multiple regressions demonstrated that N 2 O, NH 2 OH, and nitrate concentrations were highly correlated, suggesting that NH 2 OH is a potential indicator for nitrification.

Description: Radiative forcing from volcanic aerosol impacts surface temperatures; however, the background climate state also affects the response. A key question thus concerns whether constraining forcing estimates is more important than constraining initial conditions for accurate simulation and attribution of posteruption climate anomalies. Here we test whether different realistic volcanic forcing magnitudes for the 1815 Tambora eruption yield distinguishable ensemble surface temperature responses. We perform a cluster analysis on a superensemble of climate simulations including three 30-member ensembles using the same set of initial conditions but different volcanic forcings based on uncertainty estimates. Results clarify how forcing uncertainties can overwhelm initial-condition spread in boreal summer due to strong direct radiative impact, while the effect of initial conditions predominate in winter, when dynamics contribute to large ensemble spread. In our setup, current uncertainties affecting reconstruction-simulation comparisons prevent conclusions about the magnitude of the Tambora eruption and its relation to the “year without summer.”

Description: Sea surface salinity is one of the most important parameters to reconstruct in paleoclimatology, reflecting amongst others the hydrological cycle, paleo-density, ice volume, and regional and global circulation of water masses. Recent culture studies and a Red Sea field study revealed a significant positive relation between salinity and Na incorporation within benthic and planktonic foraminiferal shells. However, these studies reported varying partitioning of Na between and within the same species. The latter could be associated with ontogenetic variations, most likely spine loss. Varying Na concentrations were observed in different parts of foraminiferal shells, with especially spines and regions close to the primary organic sheet being enriched in Na. In this study, we unravel the Na composition of different components of the planktonic foraminiferal shell wall using Electron Probe Micro Analysis (EPMA) and solution-ICP-MS. A model is presented to interpret EPMA data for spines and spine bases to quantitatively assess differences in composition and contribution to whole shell Na/Ca signals. The same model can also be applied to other spatial inhomogeneities observed in foraminiferal shell chemistry, like elemental (e.g. Mg, Na, S) banding and/or hotspots. The relative contribution of shell calcite, organic linings, spines and spine bases to whole shell Na chemistry is considered quantitatively. This study shows that whereas the high Na areas may be susceptible to taphonomy, the Na chemistry of the shell itself seems relatively robust. Comparing both shell and spine Na/Ca values with salinity shows that shell chemistry records salinity, albeit with a very modest slope.

Description: Increasing global energy demands have led to the ongoing intensification of hydrocarbon extraction from marine areas. Hydrocarbon extractive activities pose threats to native marine biodiversity, such as noise, light, and chemical pollution, physical changes to the sea floor, invasive species, and greenhouse gas emissions. Here, we assessed at a global scale the spatial overlap between offshore hydrocarbon activities and marine biodiversity (〉25,000 species, nine major ecosystems, and marine protected areas), and quantify the changes over time. We discovered that two-thirds of global offshore hydrocarbon activities occur in areas within the top 10% for species richness, range rarity, and proportional range rarity values globally. Thus, while hydrocarbon activities are undertaken in less than one percent of the ocean's area, they overlap with approximately 85% of all assessed species. Of conservation concern, 4% of species with the largest proportion of their range overlapping hydrocarbon activities are range restricted, potentially increasing their vulnerability to localized threats such as oil spills. While hydrocarbon activities have extended to greater depths since the mid-1990s, we found that the largest overlap is with coastal ecosystems, particularly estuaries, saltmarshes and mangroves. Furthermore, in most countries where offshore hydrocarbon exploration licensing blocks have been delineated, they do not overlap with marine protected areas (MPAs). Although this is positive in principle, many countries have far more licensing block areas than protected areas, and in some instances, MPA coverage is minimal. These findings suggest the need for marine spatial prioritization to help limit future spatial overlap between marine conservation priorities and hydrocarbon activities. Such prioritization can be informed by the spatial and quantitative baseline information provided here. In increasingly shared seascapes, prioritizing management actions that set both conservation and development targets could help minimize further declines of biodiversity and environmental changes at a global scale.

Description: Genetic data have great potential for improving fisheries management by identifying the fundamental management units—that is, the biological populations—and their mixing. However, so far, the number of practical cases of marine fisheries management using genetics has been limited. Here, we used Atlantic cod in the Baltic Sea to demonstrate the applicability of genetics to a complex management scenario involving mixing of two genetically divergent populations. Specifically, we addressed several assumptions used in the current assessment of the two populations. Through analysis of 483 single nucleotide polymorphisms (SNPs) distributed across the Atlantic cod genome, we confirmed that a model of mechanical mixing, rather than hybridization and introgression, best explained the pattern of genetic differentiation. Thus, the fishery is best monitored as a mixed-stock fishery. Next, we developed a targeted panel of 39 SNPs with high statistical power for identifying population of origin and analyzed more than 2,000 tissue samples collected between 2011 and 2015 as well as 260 otoliths collected in 2003/2004. These data provided high spatial resolution and allowed us to investigate geographical trends in mixing, to compare patterns for different life stages and to investigate temporal trends in mixing. We found similar geographical trends for the two time points represented by tissue and otolith samples and that a recently implemented geographical management separation of the two populations provided a relatively close match to their distributions. In contrast to the current assumption, we found that patterns of mixing differed between juveniles and adults, a signal likely linked to the different reproductive dynamics of the two populations. Collectively, our data confirm that genetics is an operational tool for complex fisheries management applications. We recommend focussing on developing population assessment models and fisheries management frameworks to capitalize fully on the additional information offered by genetically assisted fisheries monitoring.

Description: Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) is a multinational program initiated in 1997 in the tropical Atlantic to improve our understanding and ability to predict ocean-atmosphere variability. PIRATA consists of a network of moored buoys providing meteorological and oceanographic data transmitted in real time to address fundamental scientific questions as well as societal needs. The network is maintained through dedicated yearly cruises, which allow for extensive complementary shipboard measurements and provide platforms for deployment of other components of the Tropical Atlantic Observing System. This paper describes network enhancements, scientific accomplishments and successes obtained from the last 10 years of observations, and additional results enabled by cooperation with other national and international programs. Capacity building activities and the role of PIRATA in a future Tropical Atlantic Observing System that is presently being optimized are also described.

Description: Parasites are one of the strongest selective agents in nature. They select for hosts that evolve counter‐adaptive strategies to cope with infection. Helminth parasites are special because they can modulate their hosts’ immune responses. This phenomenon is important in epidemiological contexts, where coinfections may be affected. How different types of hosts and helminths interact with each other is insufficiently investigated. We used the three‐spined stickleback (Gasterosteus aculeatus) – Schistocephalus solidus model to study mechanisms and temporal components of helminth immune modulation. Sticklebacks from two contrasting populations with either high resistance (HR) or low resistance (LR) against S. solidus, were individually exposed to S. solidus strains with characteristically high growth (HG) or low growth (LG) in G. aculeatus. We determined the susceptibility to another parasite, the eye fluke Diplostomum pseudospathaceum, and the expression of 23 key immune genes at three time points after S. solidus infection. D. pseudospathaceum infection rates and the gene expression responses depended on host and S. solidus type and changed over time. Whereas the effect of S. solidus type was not significant after three weeks, T regulatory responses and complement components were upregulated at later time points if hosts were infected with HG S. solidus. HR hosts showed a well orchestrated immune response, which was absent in LR hosts. Our results emphasize the role of regulatory T cells and the timing of specific immune responses during helminth infections. This study elucidates the importance to consider different coevolutionary trajectories and ecologies when studying host‐parasite interactions.

Description: Seafloor massive sulphide (SMS) deposits are of increasing economic interest in order to satisfy the relentless growth in worldwide metal demand. The Trans‐Atlantic Geotraverse (TAG) hydrothermal field at 26°N on the Mid‐Atlantic Ridge hosts several such deposits. This study presents new controlled source electromagnetic (CSEM), bathymetric and magnetic results from the TAG field. Potential SMS targets were selected based on their surface expressions in high‐resolution bathymetric data. High‐resolution reduced‐to‐the‐pole magnetic data show negative anomalies beneath and surrounding the SMS deposits, revealing large areas of hydrothermal alteration. CSEM data, sensitive to the electrical conductivity of SMS mineralization, further reveal a maximum thickness of up to 80 m and conductivities of up to 5 S/m. SMS samples have conductivities of up to a few thousand S/m, suggesting that remotely inferred conductivities represent an average of metal sulphide ores combined with silicified and altered host basalt that likely dominates at greater depths.

Description: The climate of the last two millennia was characterised by decadal to multi‐centennial variations which were recorded in terrestrial records and had important societal impacts. The cause of these climatic events is still under debate but changes in the North Atlantic circulation have often been proposed to play an important role. In this review we compile available high‐resolution paleoceanographic datasets from the northern North Atlantic and Nordic Seas. The records are grouped into regions related to modern ocean conditions and their variability is discussed. We additionally discuss our current knowledge from modelling studies, with a specific focus on the dynamical changes that are not well inferred from the proxy records. An illustration is provided through the analysis of two climate model ensembles and an individual simulation of the last millennium. This review thereby provides an up‐to‐date paleo‐perspective on the North Atlantic multidecadal to multi‐centennial ocean variability across the last two millennia.

Description: In the course of the ongoing global intensification and diversification of human pressures, the study of variation patterns of biological traits along environmental gradients can provide relevant information on the performance of species under shifting conditions. The pronounced salinity gradient, co‐occurrence of multiple stressors, and accelerated rates of change make the Baltic Sea and its transition to North Sea a suitable region for this type of study. Focusing on the bladderwrack Fucus vesiculosus, one of the main foundation species on hard‐bottoms of the Baltic Sea, we analyzed the phenotypic variation among populations occurring along 2,000 km of coasts subjected to salinities from 4 to 〉30 and a variety of other stressors. Morphological and biochemical traits, including palatability for grazers, were recorded at 20 stations along the Baltic Sea and four stations in the North Sea. We evaluated in a common modeling framework the relative contribution of multiple environmental drivers to the observed trait patterns. Salinity was the main and, in some cases, the only environmental driver of the geographic trait variation in F. vesiculosus. The decrease in salinity from North Sea to Baltic Sea stations was accompanied by a decline in thallus size, photosynthetic pigments, and energy storage compounds, and affected the interaction of the alga with herbivores and epibiota. For some traits, drivers that vary locally such as wave exposure, light availability or nutrient enrichment were also important. The strong genetic population structure in this macroalgae might play a role in the generation and maintenance of phenotypic patterns across geographic scales. In light of our results, the desalination process projected for the Baltic Sea could have detrimental impacts on F. vesiculosus in areas close to its tolerance limit, affecting ecosystem functions such as habitat formation, primary production, and food supply.

Description: Key Points: • A regional ocean model is used to examine multidecadal shelf temperature changes on the Agulhas Bank • There are distinct shelf temperature regime changes in 1966 and 1996 • These regime shifts are caused by changes in coastal upwelling linked to large-scale wind variability The Agulhas Bank is an important area for the spawning of small pelagic fish and other species. Here, within a NEMO ocean model, we investigate changes in temperature over the Bank on multidecadal time scales. In agreement with previous observational studies, a shift to colder temperatures is found in 1997. The model also simulates an earlier shift from colder to warmer temperatures in 1966. These shifts are coastally confined and shown, using a climatologically forced model run as a control, to be driven by a north‐south migration in the large‐scale wind belts, rather than by changes in downward heat fluxes or changes in the Agulhas Current itself. The zonal wind changes on the Agulhas Bank show a significant relationship with the Southern Annular Mode, showing some promise for future predictability of cold and warm regimes on the Agulhas Bank. Thus, while the Agulhas Current has been shown in previous work to have a large impact on intra‐annual and interannual temperature variability, this work shows that multidecadal variability in temperature on the shelf is likely to be wind forced.

Description: Gravitational sinking of photosynthetically fixed particulate organic carbon (POC) constitutes a key component of the biological carbon pump. The fraction of POC leaving the surface ocean depends on POC sinking velocity (SV) and remineralization rate (Cremin), both of which depend on plankton community structure. However, the key drivers in plankton communities controlling SV and Cremin are poorly constrained. In fall 2014, we conducted a 6 weeks mesocosm experiment in the subtropical NE Atlantic Ocean to study the influence of plankton community structure on SV and Cremin. Oligotrophic conditions prevailed for the first 3 weeks, until nutrient‐rich deep water injected into all mesocosms stimulated diatom blooms. SV declined steadily over the course of the experiment due to decreasing CaCO3 ballast and – according to an optical proxy proposed herein – due to increasing aggregate porosity mostly during an aggregation event after the diatom bloom. Furthermore, SV was positively correlated with the contribution of picophytoplankton to the total phytoplankton biomass. Cremin was highest during a Synechococcus bloom under oligotrophic conditions and in some mesocosms during the diatom bloom after the deep‐water addition while it was particularly low during harmful algal blooms. The temporal changes were considerably larger in Cremin (max. 15‐fold) than in SV (max. 3‐fold). Accordingly, estimated POC transfer efficiency to 1000 m was mainly dependent on how the plankton community structure affected Cremin. Our approach revealed key players and interactions in the plankton food web influencing POC export efficiency thereby improving our mechanistic understanding of the biological carbon pump. Key points Sinking velocity was higher during oligotrophy than during blooms which is linked to ballast, porosity, and phytoplankton size structure Remineralization was highly variable but tended to be higher during Synechococcus or diatom blooms and lower during harmful algal blooms Plankton community structure had a considerably larger influence on particle remineralization rate than on sinking velocity

Description: The physiological processes driving the rapid rates of calcification in larval bivalves are poorly understood. Here, we use a calcification substrate-limited approach (low dissolved inorganic carbon, CT) and mRNA sequencing to identify proteins involved in bicarbonate acquisition during shell formation. As a secondary approach, we examined expression of ion transport and shell matrix proteins (SMPs) over the course of larval development and shell formation. We reared four families of Mytilus edulis under ambient (ca. 1865 µmol/kg) and low CT (ca. 941 µmol/kg) conditions and compared expression patterns at six developmental time points. Larvae reared under low CT exhibited a developmental delay, and a small subset of contigs was differentially regulated between ambient and low CT conditions. Of particular note was the identification of one contig encoding an anion transporter (SLC26) which was strongly upregulated (2.3–2.9 fold) under low CT conditions. By analyzing gene expression profiles over the course of larval development, we are able to isolate sequences encoding ion transport and SMPs to enhance our understanding of cellular pathways underlying larval calcification processes. In particular, we observe the differential expression of contigs encoding SLC4 family members (sodium bicarbonate cotransporters, anion exchangers), calcium-transporting ATPases, sodium/calcium exchangers, and SMPs such as nacrein, tyrosinase, and transcripts related to chitin production. With a range of candidate genes, this work identifies ion transport pathways in bivalve larvae and by applying comparative genomics to investigate temporal expression patterns, provides a foundation for further studies to functionally characterize the proteins involved in larval calcification.

Description: Mid‐ocean ridge axes are marked by segmentation of the axes and underlying magmatic systems. Fine‐scale segmentation has mainly been studied along fast‐spreading ridges. Here we offer insight into the third‐ and fourth‐order segmentation of intermediate‐spreading ridges and their temporal evolution. The Alarcón Rise and the Endeavour Segment have similar spreading rates (49 and 52.5 mm/year, respectively) but contrasting morphologies that vary from an axial high with a relatively narrow axial summit trough to an axial valley. One‐meter resolution bathymetry acquired by autonomous underwater vehicles, lava geochemistry, and ages from sediment cores is combined with available seismic reflection profiles to analyze variations in (1) geometry and orientation of the axial summit trough or valley, (2) seafloor depth near the axis, and (3) distribution of hydrothermal vents, (4) lava chemistry, and (5) flow ages between contiguous axes. Along both intermediate‐spreading segments, third‐ and fourth‐order discontinuities and associated segments are similar in dimension to what has been observed along fast‐spreading ridges. The Alarcón Rise and the Endeavour Segment also allow the study of the evolution of fine‐scale segmentation over periods of 300 to 4,000 years. Comparison between old and young axes reveals that the evolution of fine‐scale segmentation depends on the intensity of the magmatic activity. High magmatic periods are associated with rapid evolution of third‐order segments, while low magmatic activity periods, dominated by tectonic deformation and/or hydrothermal activity, are associated with little to no change in segmentation.

Description: The subterranean flow of water through sand barriers between coastal lagoons and the sea, driven by a positive hydraulic gradient, is a net new pathway for solute transfer to the sea. On the sea side of sand barriers, seawater circulation in the swash-zone generates a flux of recycled and new solutes. The significance and temporal variability of these vectors to the French Mediterranean Sea is unknown, despite lagoons constituting ~ 50% of the coastline. A one-dimensional Ra-224(ex)/Ra-223 reactive-transport model was used to quantify water flow between a coastal lagoon (La Palme) and the sea over a 6-month period. Horizontal flow between the lagoon and sea decreased from ~ 85 cm d(-1) during May 2017 (0.3 m(3) d(-1) m(-1) of shoreline) to ~ 20 cm d(-1) in July and was negligible in the summer months thereafter due to a decreasing hydraulic gradient. Seawater circulation in the swash-zone varied from 10 to 52 cm d(-1) (0.4-2.1 m(3) d(-1) m(-1)), driven by short-term changes in the prevailing wind and wave regimes. Both flow paths supply minor dissolved silica fluxes on the order of ~ 3-10 mmol Si d(-1) m(-1). Lagoon-sea water exchange supplies a net dissolved inorganic carbon (DIC) flux (320-1100 mmol C d(-1) m(-1)) two orders of magnitude greater than seawater circulation and may impact coastal ocean acidification. The subterranean flow of water through sand barriers represents a significant source of new DIC, and potentially other solutes, to the Mediterranean Sea during high lagoon water-level periods and should be considered in seasonal element budgets.

Description: We study the structure and tectonics of the collision zone between the Nazca Ridge (NR) and the Peruvian margin constrained by seismic, gravimetric, bathymetric, and natural seismological data. The NR was formed in an on-ridge setting, and it is characterized by a smooth and broad shallow seafloor (swell) with an estimated buoyancy flux of ~7 Mg/s. The seismic results show that the NR hosts an oceanic lower crust 10–14 km thick with velocities of 7.2–7.5 km/s suggesting intrusion of magmatic material from the hot spot plume to the oceanic plate. Our results show evidence for subduction erosion in the frontal part of the margin likely enhanced by the collision of the NR. The ridge-trench collision zone correlates with the presence of a prominent normal scarp, a narrow continental slope, and (uplifted) shelf. In contrast, adjacent of the collision zone, the slope does not present a topographic scarp and the continental slope and shelf become wider and deeper. Geophysical and geodetic evidence indicate that the collision zone is characterized by low seismic coupling at the plate interface. This is consistent with vigorous subduction erosion enhanced by the subducting NR causing abrasion and increase of fluid pore pressure at the interplate contact. Furthermore, the NR has behaved as a barrier for rupture propagation of megathrust earthquakes (e.g., 1746 Mw 8.6 and 1942 Mw 8.1 events). In contrast, for moderate earthquakes (e.g., 1996 Mw 7.7 and 2011 Mw 6.9 events), the NR has behaved as a seismic asperity nucleating at depths 〉20 km.

Description: Due to its remoteness, the deep-sea floor remains an understudied ecosystem of our planet. The patchiness of existing data sets makes it difficult to draw conclusions about processes that apply to a wider area. In our study we show how different settings and processes determine sediment heterogeneity on small spatial scales. We sampled solid phase and porewater from the upper 10 m of an approximately 7.4×13 km2 area in the Peru Basin, in the southeastern equatorial Pacific Ocean, at 4100 m water depth. Samples were analyzed for trace metals, including rare earth elements and yttrium (REY), as well as for particulate organic carbon (POC), CaCO3, and nitrate. The analyses revealed the surprisingly high spatial small-scale heterogeneity of the deep-sea sediment composition. While some cores have the typical green layer from Fe(II) in the clay minerals, this layer is missing in other cores, i.e., showing a tan color associated with more Fe(III) in the clay minerals. This is due to varying organic carbon contents: nitrate is depleted at 2–3 m depth in cores with higher total organic carbon contents but is present throughout cores with lower POC contents, thus inhibiting the Fe(III)-to-Fe(II) reduction pathway in organic matter degradation. REY show shale-normalized (SN) patterns similar to seawater, with a relative enrichment of heavy REY over light REY, positive LaSN anomaly, negative CeSN anomaly, and positive YSN anomaly and correlate with the Fe-rich clay layer and, in some cores, also correlate with P. We therefore propose that Fe-rich clay minerals, such as nontronite, as well as phosphates, are the REY-controlling phases in these sediments. Variability is also seen in dissolved Mn and Co concentrations between sites and within cores, which might be due to dissolving nodules in the suboxic sediment, as well as in concentration peaks of U, Mo, As, V, and Cu in two cores, which might be related to deposition of different material at lower-lying areas or precipitation due to shifting redox boundaries.

Description: Global climatologies of the seawater CO2 chemistry variables are necessary to assess the marine carbon cycle in depth. The climatologies should adequately capture seasonal variability to properly address ocean acidification and similar issues related to the carbon cycle. Total alkalinity (A(T)) is one variable of the seawater CO2 chemistry system involved in ocean acidification and frequently measured. We used the Global Ocean Data Analysis Project version 2.2019 (GLODAPv2) to extract relationships among the drivers of the A(T) variability and A(T) concentration using a neural network (NNGv2) to generate a monthly climatology. The GLODAPv2 quality-controlled dataset used was modeled by the NNGv2 with a root-mean-squared error (RMSE) of 5.3 mu mol kg(-1). Validation tests with independent datasets revealed the good generalization of the network. Data from five ocean time-series stations showed an acceptable RMSE range of 3-6.2 mu mol kg(-1). Successful modeling of the monthly A(T) variability in the time series suggests that the NNGv2 is a good candidate to generate a monthly climatology. The climatological fields of A(T) were obtained passing through the NNGv2 the World Ocean Atlas 2013 (WOA13) monthly climatologies of temperature, salinity, and oxygen and the computed climatologies of nutrients from the previous ones with a neural network. The spatiotemporal resolution is set by WOA13: 1 degrees x 1 degrees in the horizontal, 102 depth levels (0-5500 m) in the vertical and monthly (0-1500 m) to annual (1550-5500 m) temporal resolution. The product is distributed through the data repository of the Spanish National Research Council (CSIC; https://doi.org/10.20350/digitalCSIC/8644, Broullon et al., 2019).

Description: Does disease resistance evolution in vitro reflect resistance evolution in vivo? Hernandez and Koskella conducted serial passage experiments of the plant pathogenic bacterium Pseudomonas syringae and two lytic bacteriophages in high‐nutrient medium (in vitro) and in a tomato plant (in vivo). High levels of bacterial resistance to phages evolved in vitro but not in vivo, suggesting that high costs and low benefits of resistance explain the observed pattern.

Description: Rationale: Nitrous oxide (N2O) is an atmospheric trace gas regulating Earth's climate, and is a key intermediate of many nitrogen cycling processes in aquatic ecosystems. Laser-based technology for N2O concentration and isotopic/isotopomeric analyses has potential advantages, which include high analytical specificity, low sample size requirement and reduced cost. Methods: An autosampler with a purge-and-trap module is coupled to a cavity ring-down spectrometer to achieve automated and high-throughput measurements of N2O concentrations, N2O isotope ratios (δ15Nbulk and δ18O values) and position-specific isotopomer ratios (δ15Nα and δ15Nβ values). The system provides accuracy and precision similar to those for measurements made by traditional isotope ratio mass spectrometry (IRMS) techniques. Results: The sample sizes required were 0.01–1.1 nmol-N2O. Measurements of four N2O isotopic/isotopomeric references were cross-calibrated with those obtained by IRMS. With a sample size of 0.50 nmol-N2O, the measurement precision (1σ) for δ15Nα, δ15Nβ, δ15Nbulk and δ18O values was 0.61, 0.33, 0.41 and 0.43‰, respectively. Correction schemes were developed for sample size-dependent isotopic/isotopomeric deviations. The instrumental system demonstrated consistent measurements of dissolved N2O concentrations, isotope/isotopomer ratios and production rates in seawater. Conclusions: The coupling of an autosampler with a purge-and-trap module to a cavity ring-down spectrometer not only significantly reduces sample size requirements, but also offers comprehensive investigation of N2O production pathways by the measurement of natural abundance and tracer level isotopes and isotopomers. Furthermore, the system can perform isotopic analyses of dissolved and solid nitrogen-containing samples using N2O as the analytical proxy.

Description: Distinct differences were observed in geochemical signatures in sediments from two sites drilled in the upper plate of the Costa Rica margin during Integrated Ocean Drilling Program (IODP) Expedition 334. The upper 80 m at Site U1379, located on the outer shelf, show pore water non‐steady state conditions characteristic of a declining methane flux. These contrast with analyses of the upper sediment layers at the middle slope site (U1378) that reflect steady state conditions. Distinct carbonate‐rich horizons up to 11 meters thick were recovered between 63 and 310 meters below seafloor at Site U1379 but were not found at Site U1378. The carbonates and dissolved inorganic carbon from Site U1379 have a depleted carbon stable isotope signal (up to ‐25‰) that indicates anaerobic methane oxidation. This inference is further supported by distinct δ34S‐pyrite and magnetic susceptibility records that reveal fluctuations of the sulfate‐methane transition in response to methane flux variations. Tectonic reconstructions of this margin document a marked subsidence event after arrival of the Cocos Ridge, 2.2 ± 0.2 million years ago (Ma), followed by increased sedimentation rates and uplift. As the seafloor at Site U1379 rose from ~2000 m to the present water depth of ~126 m, the site moved out of the gas hydrate stability zone (GHSZ) at ~1.1 Ma, triggering upward methane advection, methane oxidation, and the onset of massive carbonate formation. Younger carbonate occurrences and the non‐steady state pore profiles at Site U1379 reflect continued episodic venting likely modulated by changes in the underlying methane reservoir.

Description: The flow (flux) of climate-critical gases, such as carbon dioxide (CO2), between the ocean and the atmosphere is a fundamental component of our climate and an important driver of the biogeochemical systems within the oceans. Therefore, the accurate calculation of these air–sea gas fluxes is critical if we are to monitor the oceans and assess the impact that these gases are having on Earth's climate and ecosystems. FluxEngine is an open-source software toolbox that allows users to easily perform calculations of air–sea gas fluxes from model, in situ, and Earth observation data. The original development and verification of the toolbox was described in a previous publication. The toolbox has now been considerably updated to allow for its use as a Python library, to enable simplified installation, to ensure verification of its installation, to enable the handling of multiple sparingly soluble gases, and to enable the greatly expanded functionality for supporting in situ dataset analyses. This new functionality for supporting in situ analyses includes user-defined grids, time periods and projections, the ability to reanalyse in situ CO2 data to a common temperature dataset, and the ability to easily calculate gas fluxes using in situ data from drifting buoys, fixed moorings, and research cruises. Here we describe these new capabilities and demonstrate their application through illustrative case studies. The first case study demonstrates the workflow for accurately calculating CO2 fluxes using in situ data from four research cruises from the Surface Ocean CO2 ATlas (SOCAT) database. The second case study calculates air–sea CO2 fluxes using in situ data from a fixed monitoring station in the Baltic Sea. The third case study focuses on nitrous oxide (N2O) and, through a user-defined gas transfer parameterisation, identifies that biological surfactants in the North Atlantic could suppress individual N2O sea–air gas fluxes by up to 13 %. The fourth and final case study illustrates how a dissipation-based gas transfer parameterisation can be implemented and used. The updated version of the toolbox (version 3) and all documentation is now freely available.

Description: Dissolved organic carbon (DOC) plays critical roles in marine carbon cycling, but its sources and sinks remain uncertain. In this study, we monitored DOC exudation rates of Sargassum natans under visible light (lambda 〉 390 nm) and solar radiation. DOC release rates ranged from 7 to 10 mu g C g(biomass)(-1) hr(-1) (wet weight) under visible light, but increased to 23 to 41 mu g C g(biomass)(-1) hr(-1) when exposed to natural sunlight. Results indicate that DOC released by Sargassum could amount to 0.3 to 1.2 Tg C/year, potentially contributing significantly to the marine DOC pool in the Gulf of Mexico and Western North Atlantic. We employed the Folin-Ciocalteu phenolic content method, nuclear magnetic resonance (NMR) spectroscopy, and ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to characterize the diverse pool of organic compounds exuded from Sargassum. Results from these complementary methods showed that Sargassum release large quantities of phlorotannins, a class of polyphenols that have very similar properties to terrestrial DOC. These phlorotannins and their oxygenated phenolic derivatives exhibit a high hydrogen deficiency and functionalization (i.e., 4 to 6 oxygen atoms per aromatic ring), representing 5 to 18% of the released DOC isolated by solid phase extraction. Thus, Sargassum is the largest biological source of open ocean polyphenols recorded to date. The amount of polyphenolic DOC released by Sargassum challenges previous beliefs that all polyphenols found within the oceans are remnants of terrestrial organic matter, although the stability of phlorotannins and their derivatives needs to be further evaluated.

Description: We present a three-dimensional gas hydrate systems model of the southern Hikurangi subduction margin in eastern New Zealand. The model integrates thermal and microbial gas generation, migration, and hydrate formation. Modeling these processes has improved the understanding of factors controlling hydrate distribution. Three spatial trends of concentrated hydrate occurrence are predicted. The first trend (I) is aligned with the principal deformation front in the overriding Australian plate. Concentrated hydrate deposits are predicted at or near the apexes of anticlines and to be mainly sourced from focused migration and recycling of microbial gas generated beneath the hydrate stability zone. A second predicted trend (II) is related to deformation in the subducting Pacific plate associated with former Mesozoic subduction beneath Gondwana and the modern Pacific-Australian plate boundary. This trend is enhanced by increased advection of thermogenic gas through permeable layers in the subducting plate and focused migration into the Neogene basin fill above Cretaceous-Paleogene structures. The third trend (III) follows the northern margin of the Hikurangi Channel and is related to the presence of buried strata of the Hikurangi Channel system. The predicted trends are consistent with pronounced seismic reflection anomalies related to free gas in the pore space and strength of the bottom-simulating reflection. However, only trend I is also associated with clear and widespread seismic indications of concentrated gas hydrate. Total predicted hydrate masses at the southern Hikurangi Margin are between 52,800 and 69,800 Mt. This equates to 3.4–4.5 Mt hydrate/km2, containing 6.33 × 108–8.38 × 108 m3/km2 of methane.

Description: Global climatic changes during the last Glacial and Deglacial have been related to variations of the Atlantic Meridional Overturning Circulation (AMOC). Here, we present new and refined 231Pa/230Th down‐core profiles extending back to 30 ka BP from the northwestern Atlantic along the Atlantic Deep Western Boundary Current (DWBC), which is the main component of the southward deep backflow of the AMOC. Besides the well‐known Bermuda Rise records, available high‐resolution 231Pa/230Th data in the northwestern Atlantic are still sparse. Our new records along with reconstructions of deep water provenance from Nd isotopes constrain the timing and magnitude of past changes in AMOC from an additional northwestern Atlantic region forming a depth transect between 3000 and 4760 m water depth. Our extended and improved dataset confirms the weakening of the AMOC during deglacial cold spells such as Heinrich Event 1 and the Younger Dryas interrupted by a reinvigoration during the Bølling‐Allerød interstadial as seen in the prominent 231Pa/230Th records from the Bermuda Rise. However, in contrast to the Bermuda Rise records we find a clearly reduced circulation strength during the Last Glacial Maximum in the deep Atlantic.

Description: Gelatinous zooplankton (Cnidaria, Ctenophora, and Urochordata, namely, Thaliacea) are ubiquitous members of plankton communities linking primary production to higher trophic levels and the deep ocean by serving as food and transferring “jelly‐carbon” (jelly‐C) upon bloom collapse. Global biomass within the upper 200 m reaches 0.038 Pg C, which, with a 2–12 months life span, serves as the lower limit for annual jelly‐C production. Using over 90,000 data points from 1934 to 2011 from the Jellyfish Database Initiative as an indication of global biomass (JeDI: http://jedi.nceas.ucsb.edu, http://www.bco‐dmo.org/dataset/526852), upper ocean jelly‐C biomass and production estimates, organism vertical migration, jelly‐C sinking rates, and water column temperature profiles from GLODAPv2, we quantitatively estimate jelly‐C transfer efficiency based on Longhurst Provinces. From the upper 200 m production estimate of 0.038 Pg C year−1, 59–72% reaches 500 m, 46–54% reaches 1,000 m, 43–48% reaches 2,000 m, 32–40% reaches 3,000 m, and 25–33% reaches 4,500 m. This translates into ~0.03, 0.02, 0.01, and 0.01 Pg C year−1, transferred down to 500, 1,000, 2,000, and 4,500 m, respectively. Jelly‐C fluxes and transfer efficiencies can occasionally exceed phytodetrital‐based sediment trap estimates in localized open ocean and continental shelves areas under large gelatinous blooms or jelly‐C mass deposition events, but this remains ephemeral and transient in nature. This transfer of fast and permanently exported carbon reaching the ocean interior via jelly‐C constitutes an important component of the global biological soft‐tissue pump, and should be addressed in ocean biogeochemical models, in particular, at the local and regional scale.

Description: Sea surface salinity (SSS) is an important variable in the global ocean circulation. However, decadal to interdecadal changes in SSS are not well understood due to the lack of instrumental data. Here we reconstruct SSS from a paired, bimonthly resolved coral δ18O and Sr/Ca record from La Reunion Island that extends from 1913 to 1995. Coral Sr/Ca correlates with regional sea surface temperature (SST) back to 1966, when instrumental coverage is good, while coral δ18O does not. The slope of the monthly (annual mean) coral Sr/Ca-SST regression is −0.040 mmol/mol per 1 °C (−0.068 mmol/mol per 1 °C) consistent with published estimates of the Sr/Ca-SST relationship. Coral Sr/Ca suggest a warming of 0.39 °C since 1913. δ18O seawater is calculated by subtracting the temperature component from measured coral δ18O, using coral Sr/Ca as well as historical SST products. The derived δ18O seawater reconstructions are correlated (r 〉 0.6), and all show a significant shift in the midtwentieth century (−0.17‰ to −0.19‰), indicating a freshening of SSS by 0.7 psu. However, the timing of this shift depends on the temperature component and varies from 1947 (δ18O seawater calculated with historical SST) to the late 1950s (δ18O seawater calculated with coral Sr/Ca). Coral Sr/Ca shows warm temperature anomalies in the mid-1950s, while historical SST products show warm anomalies from 1940 to 1945 followed by cooling in the 1950s, a pattern typical for the World War II bias. This suggests that historical SST may bias reconstructions of δ18O seawater and SSS from corals.

Description: Climate reconstructions are means to extract the signal from uncertain paleo-observations, so-called proxies. It is essential to evaluate these reconstructions to understand and quantify their uncertainties. Similarly, comparing climate simulations and proxies requires approaches to bridge the temporal and spatial differences between both and to address their specific uncertainties. One way to achieve these two goals is so-called pseudoproxies. These are surrogate proxy records within the virtual reality of a climate simulation. They in turn depend on an understanding of the uncertainties of the real proxies including the noise characteristics disturbing the original environmental signal. Common pseudoproxy approaches so far concentrate on data with high temporal resolution over the last approximately 2000 years. Here we provide a simple but flexible noise model for potentially low-resolution sedimentary climate proxies for temperature on millennial timescales, the code for calculating a set of pseudoproxies from a simulation, and one example of pseudoproxies. The noise model considers the influence of other environmental variables, a dependence on the climate state, a bias due to changing seasonality, modifications of the archive (for example bioturbation), potential sampling variability, and a measurement error. Model, code, and data allow us to develop new ways of comparing simulation data with proxies on long timescales. Code and data are available at https://doi.org/10.17605/OSF.IO/ZBEHX (Bothe et al., 2018).

Description: Atmospheric deposition is an important source of micronutrients to the ocean, but atmospheric deposition fluxes remain poorly constrained in most ocean regions due to the limited number of field observations of wet and dry atmospheric inputs. Here we present the distribution of dissolved aluminium (dAl), as a tracer of atmospheric inputs, in surface waters of the Atlantic Ocean along GEOTRACES sections GA01, GA06, GA08, and GA10. We used the surface mixed layer concentrations of dAl to calculate atmospheric deposition fluxes using a simple steady state model. We have optimized the aerosol Al fractional solubility, dAl residence time within the surface mixed layer and depth of the surface mixed layer for each separate cruise to calculate the atmospheric deposition fluxes. We calculated the lowest deposition fluxes of 0.15 ± 0.1 and 0.27 ± 0.13 g m−2 yr−1 for the South and North Atlantic Ocean (〉 40° S and 〉 40° N), respectively, and highest fluxes of 2.67 ± 1.96 and 3.82 ± 2.72 g m−2 yr−1 for the South East Atlantic and tropical Atlantic Ocean, respectively. Overall, our estimations are comparable to atmospheric dust deposition model estimates and reported field-based atmospheric deposition estimates. We note that our estimates diverge from atmospheric dust deposition model flux estimates in regions influenced by riverine Al inputs and in upwelling regions. As dAl is a key trace element in the GEOTRACES Programme, the approach presented in this study allows calculations of atmospheric deposition fluxes at high spatial resolution for remote ocean regions.

Description: Aim: Numerous regions worldwide are highly impacted by anthropogenic activities and globalization, with climate change and species introductions being among the greatest stressors to biodiversity and ecosystems. A main donor region of non‐indigenous species (NIS) for numerous European water bodies, as well as in the North American Great Lakes is the Ponto‐Caspian region (i.e., Black, Azov and Caspian Seas), with some of those species having significant impact on local communities and ecosystem functioning. Location: Northern European, Ponto‐Caspian and North American regions. Methods: To determine environmental tolerance of native species and related NIS under current and future global warming scenarios of the Baltic Sea, we conducted common garden experiments to test temperature tolerance of three euryhaline gammarid species: one Baltic (Gammarus oceanicus), one Ponto‐Caspian (Pontogammarus maeoticus) and one North American species (Gammarus tigrinus) in two different salinities. Results: Our results determined that mortality of P. maeoticus in all temperature treatments (i.e., increased, control, and decreased) at the end of both experiments (i.e., conducted in salinities of 10 and 16 g/kg) was lower when compared to mortality of G. oceanicus and (c) G. tigrinus. The highest mortality was observed for G. oceanicus, reaching 100% in both experiments in the increased temperature treatment. Main conclusions: Due to the high environmental tolerance of the Ponto‐Caspian species tested in this study, as well as the fact that Ponto‐Caspian species evolved in environmentally variable habitats and currently inhabit warmer waters than species from North America and Northern Europe, we suggest that species from the Ponto‐Caspian region may benefit from global warming when invading new areas. Those new invasions may, in the best case scenario, increase biodiversity of the Baltic Sea. However, if notorious invaders arrive, they may have a significant impact on local communities and ecosystem functioning.

Description: Reconstruction of early Cenozoic deep‐water circulation is one of the keys to modelling Earth's greenhouse‐to‐icehouse surface evolution, but it has long been hampered by the paucity of information from the central South Pacific. To help overcome this knowledge gap, we present new micropalaeontological data from dredged carbonates (R/V Sonne Expedition SO193) at several eastern volcanic salients of the Manihiki Plateau. Interestingly, despite appreciable longitudinal separations among the dredged sites, ages indicated by the foraminiferal assemblages are consistently around the Middle Eocene [including mixed Turonian (Late Cretaceous)/Eocene at a single site], suggesting widespread post‐Eocene cessation of the pelagic sedimentation. By integrating with independent seismic and chronostratigraphic data (Deep Sea Drilling Project Leg 33) for large‐scale erosion of top‐Eocene–Oligocene sedimentary units on the eastern Manihiki Plateau, our results can be viewed as novel physical evidence for the intensification of central South Pacific deep‐water circulation since the Eocene/Oligocene climatic transition.

Description: The nature of the Ionian Sea crust has been the subject of scientific debate for more than 30 years, mainly because seismic imaging of the deep crust and upper mantle of the Ionian Abyssal Plain (IAP) has not been conclusive to date. The IAP is sandwiched between the Calabrian and Hellenic subduction zones in the central Mediterranean. To univocally confirm the proposed oceanic nature of the IAP crust as a remnant of the Tethys ocean and to confute its interpretation as a strongly thinned part of the African continental crust, a NE-SW oriented 131 km long seismic refraction and wide-angle reflection profile consisting of eight ocean bottom seismometers and hydrophones was acquired in 2014. A P-wave velocity model developed from travel time forward modelling is refined by gravimetric data and synthetic modelling of the seismic data. A roughly 6km thick crust with velocities ranging from 5.1km/s to 7.2km/s, top to bottom, can be traced throughout the IAP. In the vicinity of the Medina Seamounts at the southern IAP boundary, the crust thickens to about 9km and seismic velocities decrease to 6.8km/s at the crust-mantle boundary. The seismic velocity distribution and depth of the crust-mantle boundary in the IAP document its oceanic nature, and support the interpretation of the IAP as a remnant of the Tethys oceanic lithosphere formed during the Permian and Triassic period.

Description: We describe the development of the “Paleoclimate PLASIM-GENIE emulator” PALEO-PGEM and its application to derive a downscaled high-resolution spatiotemporal description of the climate of the last five million years. The 5-million-year time frame is interesting for a range of paleo-environmental questions, not least because it encompasses the evolution of humans. However, the choice of time-frame was primarily pragmatic; tectonic changes can be neglected to first order, so that it is reasonable to consider climate forcing restricted to the Earth's orbital configuration, ice-sheet state and the concentration of atmosphere CO2. The approach uses the Gaussian process emulation of the singular value decomposition of boundary-condition ensembles of the intermediate complexity atmosphere-ocean GCM PLASIM-GENIE. Spatial fields of bioclimatic variables of surface air temperature (warmest and coolest seasons) and precipitation (wettest and driest seasons) are emulated at 1,000 year intervals, driven by time-series of scalar boundary-condition forcing (CO2, orbit and ice-volume), and assuming the climate is in quasi-equilibrium. Paleoclimate anomalies at climate model resolution are interpolated onto the observed modern climatology to produce a high-resolution spatiotemporal paleoclimate reconstruction of the Pliocene-Pleistocene.

Description: The interaction between the atmosphere, specifically the North Atlantic Oscillation (NAO), and the North Atlantic ocean circulation on sub‐decadal timescale is analyzed in a subset of models participating in the Coupled Model Intercomparison Project phase 5 (CMIP5). From preindustrial control runs of at least 500 years length, we derive anomaly patterns in the atmospheric and ocean circulation and of air‐sea heat exchange. All models simulate a distinct dipolar oceanic overturning anomaly at the sub‐decadal timescale, with centers at 30° N and 55° N. The dipolar overturning anomaly goes along with marked anomalies in the North Atlantic sea surface temperature and gyre circulation. Lag‐regression analyses demonstrate, with relatively small ensemble spread, how the atmosphere and the ocean circulation interact. The dipolar anomalies in the overturning are forced by NAO‐related wind stress curl anomalies. Anomalous surface heat fluxes in concert with anomalous vertical motions drive a meridional dipolar heat content anomaly in the upper ocean, and it is this dipolar heat content anomaly which carries the coupled system from one phase of the sub‐decadal cycle to the other by reversing the tendencies in the overturning circulation. The coupled sub‐decadal variability derived from the CMIP5 models is characterized by three elements: a wind‐driven part steering the dipolar overturning anomaly, surface heat flux anomalies that support a heat build‐up in the subpolar gyre region, and the heat storage memory which is instrumental in the phase reversal of the NAO.

Description: Long-term measurements of volcanic gas emissions conducted during the recent decade suggest that under certain conditions the magnitude or chemical composition of volcanic emissions exhibits periodic variations with a period of about two weeks. A possible cause of such a periodicity can be attributed to the Earth tidal potential. The phenomenology of such a link has been debated for long, but no quantitative model has yet been proposed. The aim of this paper is to elucidate whether a causal link from the tidal forcing to variation in the volcanic degassing can be traced analytically. We model the response of a simplified magmatic system to the local tidal gravity variations and derive a periodical vertical magma displacement in the conduit with an amplitude of 0.1–1 m, depending on geometry and physical state of the magmatic system. We find that while the tide-induced vertical magma displacement has presumably no significant direct effect on the volatile solubility, the differential magma flow across the radial conduit profile may result in a significant increase of the bubble coalescence rate in a depth of several kilometres by up to several ten percent. Because bubble coalescence facilitates separation of gas from magma and thus enhances volatile degassing, we argue that the derived tidal variation may propagate to a manifestation of varying volcanic degassing behaviour. The presented model provides a first basic framework which establishes an analytical understanding of the link between the Earth tides and volcanic degassing.

Description: Ground-based atmospheric observations of CO2, δ(O2∕N2), N2O, and CH4 were used to make estimates of the air–sea fluxes of these species from the Lüderitz and Walvis Bay upwelling cells in the northern Benguela region, during upwelling events. Average flux densities (±1σ) were 0.65±0.4 µmol m−2 s−1 for CO2, −5.1±2.5 µmol m−2 s−1 for O2 (as APO), 0.61±0.5 nmol m−2 s−1 for N2O, and 4.8±6.3 nmol m−2 s−1 for CH4. A comparison of our top-down (i.e., inferred from atmospheric anomalies) flux estimates with shipboard-based measurements showed that the two approaches agreed within ±55 % on average, though the degree of agreement varied by species and was best for CO2. Since the top-down method overestimated the flux density relative to the shipboard-based approach for all species, we also present flux density estimates that have been tuned to best match the shipboard fluxes. During the study, upwelling events were sources of CO2, N2O, and CH4 to the atmosphere. N2O fluxes were fairly low, in accordance with previous work suggesting that the evasion of this gas from the Benguela is smaller than for other eastern boundary upwelling systems (EBUS). Conversely, CH4 release was quite high for the marine environment, a result that supports studies that indicated a large sedimentary source of CH4 in the Walvis Bay area. These results demonstrate the suitability of atmospheric time series for characterizing the temporal variability of upwelling events and their influence on the overall marine greenhouse gas (GHG) emissions from the northern Benguela region.

Description: Rationale Boron (B) is an essential micronutrient in plants and its isotope variations are used to gain insights into plant metabolism, which is important for crop plant cultivation. B isotope variations were used to trace intraplant fractionation mechanisms in response to the B concentration in the irrigation water spanning the range from B depletion to toxic levels. Methods A fully validated analytical procedure based on MC‐ICP‐MS, sample decomposition and B matrix separation was applied to study B isotope fractionation. The validation was accomplished by establishing a complete uncertainty budget and by applying reference materials, yielding expanded measurement uncertainties of 0.8 ‰ for pure boric acid solutions and ≤ 1.5 ‰ for processed samples. With this validated procedure SI traceable B isotope amount ratios were determined in plant reference materials for the first time. Results The B isotope compositions of irrigation water and bell pepper samples suggest passive diffusion of the heavy 11B isotope into the roots during low to high B concentrations while uptake of the light 10B isotope was promoted during B depletion, probably by active processes. A systematic enrichment of the heavy 11B isotope in higher located plant parts was observed (average Δ11Bleaf‐roots = 20.3 ± 2.8 ‰ (1 SD)), possibly by a facilitated transport of the heavy 11B to growing meristems by B transporters. Conclusions B isotopes can be used to identify plant metabolism in response to the B concentration in the irrigation water and during intraplant B transfer. The large B isotope fractionation within the plants demonstrates the importance of biological B cycling for the global B cycle.

Description: Recent studies using reanalysis data and complex models suggest that the Tropics influence midlatitude blocking. Here, the influence of tropical precipitation anomalies is investigated further using a dry dynamical model driven by specified diabatic heating anomalies. The model uses a quasi‐realistic setup based on idealized orography and an idealized representation of the land‐ocean thermal contrast. Results concerning the El Niño Southern Oscillation and the Madden‐Julian Oscillation are mostly consistent with previous studies and emphasize the importance of tropical dynamics for driving the variability of blocking at midlatitudes. It is also shown that a common bias in models of the Coupled Model Intercomparison Project Phase 5 (CMIP5), namely, excessive tropical precipitation, leads to an underestimation of midlatitude blocking in our model, also a common bias in the CMIP5 models. The strongest blocking anomalies associated with the tropical precipitation bias are found over Europe, where the underestimation of blocking in CMIP5 models is also particularly strong.

Description: Key Points: - Rapid subsurface oceanographic change in the tropical W Atlantic reflect shifting Subtropical Gyre - Subsurface warming responds to deglacial AMOC perturbations (Heinrich Stadials 2, 1, and the Younger Dryas) - Southward propagation of Salinity Maximum Water during Northern Hemisphere cold spells shift the mixing zone of tropical and subtropical waters During times of deglacial Atlantic Meridional Overturning Circulation (AMOC) perturbations, the tropical Atlantic experienced considerable warming at subsurface levels. Coupled ocean‐atmosphere simulations corroborate the tight teleconnection between the tropical Atlantic and climate change at high northern latitudes, but still underestimate the relevance of the subsurface N Atlantic Subtropical Gyre (STG) for heat and salt storage and its sensitivity to rapid climatic change. We here reconstruct vertical and lateral temperature and salinity gradients in the tropical W Atlantic and the Caribbean over the last 30 kyrs, based on planktic deep and shallow dwelling foraminiferal Mg/Ca and δ18O‐records. The rapid and large amplitude subsurface changes illustrate a dynamic STG associated with abrupt shifts of North Atlantic hydrographic and atmospheric regimes. During full glacial conditions, the STG has been shifted southward while intensified Ekman‐downwelling associated to strengthened trade winds fostered the formation of warm and saline Salinity Maximum Water (SMW). The southward propagation of SMW was facilitated by the glacially eastward deflected North Brazil Current. During periods of significant AMOC perturbations (Heinrich Stadials 1, and the Younger Dryas), extreme subsurface warming by ~6°C led to diminished lateral subsurface temperature gradients. Coevally, a deep thermocline suggests that SMW fully occupied the subsurface tropical W Atlantic and that the STG reached its southernmost position. During the Holocene, modern‐like conditions gradually developed with the northward retreat of SMW and the development of a strong thermocline ridge between the Subtropical Gyre and the tropical W Atlantic.

Description: Quaternary East Asian winter monsoon (EAWM) evolution has long been attributed to high-latitude Northern Hemisphere climate change. However, it cannot explain the distinct relationships of the EAWM in the northern and southern East Asian marginal sea in paleoclimatic records. Here we present an EAWM record of the northern East China Sea over the past 300 ka and a transient climate simulation with the Kiel Climate Model through the Holocene. Both proxy record and simulation suggest anticorrelated long-term EAWM evolution between the northern East China Sea and the South China Sea. We suggest that this spatial discrepancy of EAWM can be interpreted as El Niño–Southern Oscillation (ENSO)-like controlling, which generates cyclonic/anticyclonic wind anomalies in the northern/southern East Asian marginal sea. This research explains much of the controversy in nonorbital scale variability of Quaternary EAWM records in the East Asian marginal sea and supports a potent role of tropical forcing in East Asian winter climate change.

Description: The atmospheric CO2 concentration increased by about 20ppm from 6000BCE to the pre-industrial period (1850CE). Several hypotheses have been proposed to explain mechanisms of this CO2 growth based on either ocean or land carbon sources. Here, we apply the Earth system model MPI-ESM-LR for two transient simulations of climate and carbon cycle dynamics during this period. In the first simulation, atmospheric CO2 is prescribed following ice-core CO2 data. In response to the growing atmospheric CO2 concentration, land carbon storage increases until 2000BCE, stagnates afterwards, and decreases from 1CE, while the ocean continuously takes CO2 out of the atmosphere after 4000BCE. This leads to a missing source of 166Pg of carbon in the ocean-land-atmosphere system by the end of the simulation. In the second experiment, we applied a CO2 nudging technique using surface alkalinity forcing to follow the reconstructed CO2 concentration while keeping the carbon cycle interactive. In that case the ocean is a source of CO2 from 6000 to 2000BCE due to a decrease in the surface ocean alkalinity. In the prescribed CO2 simulation, surface alkalinity declines as well. However, it is not sufficient to turn the ocean into a CO2 source. The carbonate ion concentration in the deep Atlantic decreases in both the prescribed and the interactive CO2 simulations, while the magnitude of the decrease in the prescribed CO2 experiment is underestimated in comparison with available proxies. As the land serves as a carbon sink until 2000BCE due to natural carbon cycle processes in both experiments, the missing source of carbon for land and atmosphere can only be attributed to the ocean. Within our model framework, an additional mechanism, such as surface alkalinity decrease, for example due to unaccounted for carbonate accumulation processes on shelves, is required for consistency with ice-core CO2 data. Consequently, our simulations support the hypothesis that the ocean was a source of CO2 until the late Holocene when anthropogenic CO2 sources started to affect atmospheric CO2.

Description: New marine geophysical data acquired across the partly ice‐covered northern East Greenland continental margin highlight a complex interaction between tectonic and magmatic events. Breakup‐related lava flows are imaged in reflection seismic data as seaward dipping reflectors (SDRs), which are found to decrease in size both northwards and southwards from a central point at 75° N. We provide evidence that the magnetic anomaly pattern in the shelf area is related to volcanic phases and not to the presence of oceanic crust. The remnant magnetization of the individual lava flows is used to deduce a relative timing of the emplacement of the volcanic wedges. We find that the SDRs have been emplaced over a period of 2‐4 Ma progressively from north to south and from landward to seaward. The new data indicate a major post‐middle Eocene magmatic phase around the landward termination of the West Jan Mayen Fracture Zone. This post‐40 Ma volcanism likely was associated with the progressive separation of the Jan Mayen microcontinent from East Greenland. The break‐up of the Greenland Sea started at several isolated seafloor spreading cells whose location was controlled by rift structures and led to the present‐day segmentation of the margin. The original rift basins were subsequently connected by steady‐state seafloor spreading that propagated southwards, from the Greenland Fracture Zone to the Jan Mayen Fracture Zone. Key Points Polyphase Cenozoic volcanic rifting and consecutive emplacement of breakup‐related lava flows units along the northern East Greenland margin Breakup along restricted margin segments is followed by north to south directed progressive opening of the Greenland Sea Widespread post‐middle Eocene (〈 40 Ma) offshore magmatism, associated with the breakup of the Jan Mayen microcontinent from East Greenland